Before we go any further, I think it is important to note how haste calculations are conducted. To find the cast time of a spell with X% haste, simply divide the original cast time of the spell by 1.X, as in the Flash Heal example above. If there are multiple haste effects then the calculation becomes more complicated. Generally, haste effects apply multiplicatively, so if you have 6% haste from enlightenment and 20% haste from gear, then the cast time of your Flash Heal will be 1.5/(1.2*1.06) = 1.18. This means that the 6% haste from Enlightenment and 20% haste from gear are collectively worth 1.2*1.06 = 1.272, or 27.2% haste, not 20% + 6% = 26%. However, not all haste effects are multiplicative, so one must be careful when calculating cast times with multiple haste effects. Eventually it would be nice to compile a list here of all possible haste effects and if they are multiplicative or additive, but I have no such list as of yet.
- Effect on throughput
- Raid healing
- Tank healing
- Relative to Spell Power and Crit
- Spells with cooldowns
- Effect on mana consumption
- Effect on reaction speed
In progress or need help with:
-There is more to say about haste and Holy priests, but Holy is not my expertise so I need some help there
I. The effect of haste on throughput.
The classic way to measure this is by the effect of haste on a certain spells HPS (health per second).
Letâ€™s say your Flash Heal heals for 5000 health on average.
An unhasted Flash Heal has a 1.5 second cast time, giving an HPS of 5000/1.5 = 3333 HPS.
If you have 30% haste, the cast time becomes 1.5/(1.3) = 1.15 seconds.
The HPS of your Flash Heal is now 5000/1.15 = 4348 HPS.
Now, for a general rule we can say that 1% haste equals 1% higher HPS: 4348 is 30% larger than 3333. There are some exceptions to this rule, but in most cases this is sound, and will be referred to in the rest of this post as the â€œ1%:1% ruleâ€.
Clarification: when I say that 1% haste increases HPS by 1%, I mean that it increases your HPS by 1% of your unhasted HPS. What this means is that going from 30% haste to 31% haste yields an increase equal to 1% of your unhasted HPS, not 1% of your 30% hasted HPS. So when you go from 30% haste to 31% haste, what you will actually see in game is really a 0.01/1.30 = 0.77% increase in HPS. Therefore one could say that haste does not scale with itself, and that the value of adding haste decreases with the more haste that you already have.
This "diminushing relative value" means that stacking only one stat is usually counter-productive.
The 1%:1% rule can be extended from individual casts to sequences of casts, assuming that as the amount of haste in question changes it does not also change the choice of spells used or their order:
See Elimbra's post for the proof.
Outside of granularity questions, adding 1% haste increases your throughput of 1% of your spammable throughput, where spammable throughput means the throughput you can obtain when casting only cd-free spells.
It should be noted that once the cast time of a spell has reached 1 second, any further haste will not increase the HPS of that spell in the strict sense of over a series of casts, because the next spell cannot be cast until 1 second after the previous spell began casting (once the Global Cool Down, or GCD, has finished). However, there is still some benefit to haste past that 1 second mark. For instance, consider two heals, spells â€œAâ€ and â€œBâ€, which are identical in every way except that spell â€œAâ€ has a 1 second cast time and spell â€œBâ€ is instant cast. In the long run, chain casts of either spell will have the same HPS, but we can all agree that an instant cast is much more valuable than a spell with a cast time. In that same way, a 0.9 second Flash Heal is slightly more valuable than a 1.0 second Flash Heal, even though your HPS over the course of the encounter will not differ.
Another way to think of how haste increases throughput is that it allows one to cast more spells in a given length of time. For instance, with zero haste you can cast 10 Flash Heals in 15 seconds. If you have 50% haste you can cast 15 Flash Heals in those 15 seconds. This is essentially the same argument as the HPS example shown above, just stated differently.
A. Holy Priests
One of the in vogue styles of play for Holy Priests at the moment is as a renew-centric raid healer, with spell casts consisting primarily of Renew, Prayer of Mending (PoM), Circle of Healing (CoH), Flash Heal (FH) and Prayer of Healing (PoH). Renew, PoM, CoH and FH fall under the 1%:1% rule up to a haste value of 50%. PoH falls under the 1%:1% rule up to a haste value of 300% for non-Serendipity hasted casts, or 221% for fully Serendipity hasted casts. PoM and CoH are also special cases due to their cooldowns, which will be addressed in section I.D of this post.
B. Discipline Priests
Discipline priests are often asked to wear two different hats depending on the encounter, raid makeup and personal preference. One must keep in mind the innate 6% haste given by 3/3 Enlightenment, which all PvE Discipline Priests should have. The haste granted by Borrowed Time following a PWS cast is important for this discussion. Assuming 5/5 in the talent, which all Discipline priests should have, the first spell cast within 5 seconds following at PWS gets an additional 25% haste. Note that instant cast spells (and Penance) do not consume the BT buff, although most appear to benefit from it in regards to reducing the GCD they generate. This means a priest can cast a PWS, then a Penance, then a Greater Heal and have both Penance and GH benefit from the 25% haste. I believe all instant casts benefit from the haste, but there have been some reports that maybe PoM does not.
The haste from Borrowed Time is what gives rise to the idea of a haste â€œsoft capâ€ for Discipline priests: the amount of haste one needs from gear to reach a 1 second GCD with BT haste up. This soft cap varies depending on raid buffs. Assuming all applicable raid buffs (BT haste â€“ 25%, 3/3 Enlightenment â€“ 6%, Wrath of Air totem â€“ 5%, Swift Retribution or Improved Moonkin â€“ 3%, but not Power Infusion or Heroism/Bloodlust), this soft cap can be derived as follows:
1.5/(1.25*1.06*1.05*1.03*X) = 1
X = 1.0468 = 4.68% haste
1% haste = 32.79 haste rating
4.68% haste = 154 haste rating
1. Tank Healing
There are two common approaches to tank healing which differ by choice of â€œfillerâ€ spell: FH or Greater Heal (GH). Like a holy priest, Flash Heal falls under the 1%:1% rule up to a value of 50% haste. Greater Heal falls under the 1%:1% rule up to a value of 300% haste (or 250% haste if 5/5 Divine Fury). Penance falls under the 1%:1% rule up to a value of 100% haste.
2. Raid healing
This role typically means heavy use of PWS, which in turn means high uptime of BT haste. If two or more PWS are cast in a row (and less than 5 seconds apart), then any haste rating you have beyond 154 is wasted on each PWS after the first. This also applies if you weave in a PoM in place of a PWS. However, even while raid healing BT haste will probably not apply to every single spell cast, nor can we assume that every spell cast will have a 1.5 second base cast time. A raid healing Discipline Priest still uses Penance (2 second base cast) and PoH (3 second base cast), which will benefit from additional haste past 154 rating even when BT is up. Flash Heal will still benefit from additional haste rating past 154 in that the heal will land sooner, but the GCD it triggers will still be capped at 1 second.
C. Haste Relative to Spell Power and Critical Strike Rating
In order to appreciate the value of haste, it is necessary to consider it in the context of its, for lack of a better word, competitors. Also, since most of the arguments on this board regarding haste tend to take the form of â€œshould I stack haste or crit or spell power?â€ this post would be remiss not to address it.
In this section we will only consider the increase to throughput provided by the three stats. Weâ€™ve already seen that 1% haste provides a 1% increase in HPS. However, 1% critical strike provides a 0.5% increase in average HPS if you are Holy, and 0.95% increase in average HPS if you are Discipline (due to Divine Aegis).
Your Flash Heal heals for an average of 5000.
If you gain 1% crit your Flash Heal now heals for an average of (5000*.99 + 5000*1.5*.01) = 5025.
And 5025/5000 = 1.005, or a 0.5% increase.
For Discipline the calculation becomes (5000*.99 + 5000*1.95*.01) = 5047.5, and 5047.5/5000 = 1.0095, or a 0.95% increase.
One can argue that the DA shield is less likely to overheal than the crit heal itself and therefore the value of crit to a Discipline priest is actually higher than 0.95%, but that argument is beyond the scope of this post.
It should also be noted that the value of Critical Strike Rating decreases when taking into account that Renew cannot crit (outside of Empowered Renew), and PWS cannot crit (outside of the glyph). And of course arguments can be made against the value of Critical Strike Rating due to the unreliable nature of critical heals and their higher chance to overheal.
Spell power is a little trickier because different spells have different coefficients and increased spell power will provide no benefit to heal that already partly or completely overheals. A full listing of Priest spell coefficients can be found at Spell power coefficient - WoWWiki - Your guide to the World of Warcraft.
Spell power is widely regarded as the largest throughput increasing stat, but the exact value of a certain amount of spell power in terms of HPS improvement is hard to quantify. The strength of spell power is also noticeable in that every spell you cast (ignoring dispels and the like) will take advantage of spell power, however not every spell will take advantage of haste or crit (as in the PWS and renew examples cited earlier).
We cannot neglect the itemization cost of the three stats. Haste rating and Critical Strike rating have equal 1.00 StatMods when it comes to item budgets. However, the conversion between rating and percentage are different between the two. Specifically, 32.79 haste rating equals 1% haste, while 45.91 crit rating equals 1% crit. This means that crit rating is 40% (45.91/32.79) more expensive than haste rating. So when considering gems/gear, note that the choice is not between 1% haste or 1% crit, but rather between 1.4% haste and 1.0% crit.
Spell power has a StatMod rating of 0.86, meaning that for every 1 haste or crit rating a piece of gear has, it could have 1.16 spell power (1/0.86).
The interdependency of the three stats should also be noted.
The most important thing to keep in mind is that spellpower, crit, and haste all increase the value of each other as you gain more. Adding more spellpower makes haste more valuable. Adding haste makes spellpower more valuable - at least for a holy priest - as has been mentioned, disc priests are limited in the value they can extract from haste. There are definitely points at which a point of haste will be more valuable in terms of HPS than a point of spellpower for a holy priest.
D. Spells with Cool Downs
The value of haste also depends on if the spell you are using has a cool down. For instance, adding haste will make Penance cast faster, but no amount of haste will allow you to cast more Penances in a given amount of time. That extra time gained from a faster Penance can be put toward filler spells, but not towards more Penances.
Adding haste means casting more spells in a given amount of time. Because the number of Cool Down spells is capped for that length of time, the extra spells must be "filler spells" like Renew or Flash Heal. This means that the ratio of CD spells to filler spells will decrease with increasing haste.
We can all agree that our CD spells (PoM, CoH, Penance) are superior to our "filler spells," so as the ratio changes to favor more filler spells it makes sense that the HPS gain will not be as large as anticipated.
Example (courtesy of RootBreaker)
Your renew heals for 18k over its duration and your circle of healing heals for 26k (both pre-overheal). If you have no haste, you can fit 3 renews between each circle of healing, doing 80K healing every 6 seconds. If you have 25% haste, your global is 1.2 seconds and you can fit 4 renews between each circle of healing, doing 98k healing every 6 seconds. In this example, 25% haste gives you a 25% increase in the number of spells you can cast, but only a 22.5% increase in healing.
The exact effect of CD spells on devaluing haste depends on the relative strengths of the CD spell and the filler spells. We can assume our CD spells are stronger (otherwise we wouldn't be casting them), so generally speaking the value of haste to us will be somewhat less than 1%:1%, but the exact difference will vary.
II. Effect on Mana Consumption
Although mana consumption is of little concern in the current tier of content, it has been an important factor in the past and will supposedly be important again in Cataclysm, therefore I think it prudent to include this section on how haste affects mana consumption.
A. More casts One argument that is occasionally made, and that we must pay heed to, is that adding haste can have a negative effect on longevity. If haste allows one to cast more spells in a given length of time, those additional spells cost mana that would not have been spent if the player did not have that haste. The haste, therefore, essentially had a negative mp5 effect.
There are some counterarguments to this negative mp5 theory. For a given fight there will only be a certain amount of damage to be healed. If we assume that all of that damage is healed (everyone survives the fight and is at full HP at the end), then additional spells allowed by more haste are actually not needed, and therefore do not need to be cast and would not result in extra mana spent. Of course, that makes certain assumptions that are perhaps not very accurate, namely that the healers play as efficiently as possible.
B. Reduced Overhealing Theoretically, haste should also reduce overhealing and therefore increase mana efficiency. Think of it like this, if every heal that everyone in the raid has is instant cast, then there is no chance of a different persons heal landing on your target while you are still casting, so overhealing would be minimized. However, I don't think we play with enough haste for anything approaching that kind of effect to occur.
Also, just because your heal lands before a heal from another healer does not really mean reduced overhealing, just a shifting of the overheal from you to the other healer, so no mana is saved.
C. Holy Concentration Uptime In a more specific case for Holy Priests, increasing one's haste allows more casts in a given length of time. More casts means more opportunities to crit, which should mean a higher uptime on Holy Concentration.
The size of this effect is of questionable value, as pointed out by Elimbras here. Essentially, higher HC uptime due to increased haste should be seen as simply a minor fringe benefit, with 1% haste giving only a few additional mp5. Gearing for crit rating and adjusting spell usage to more non-SoL FH/GH/Renew/BH would provide much larger increases in HC uptime.
III. Effect on Reaction Speed
One of the most common arguments seen on these boards is that haste saves lives. This is commonly stated as something like,
I often have my target die a split second before my heal lands, but rarely because does my target die because my heal needed to be a few hundred HP bigger, therefore adding haste is better than adding spell power or crit.
That increased haste should result in more saved lives seems obvious and needs no proof, but to say that adding haste will save more lives than adding spell power does requires some supporting evidence. Unfortunately, this kind of claim is something that would require the intricate analysis of large amounts of data, which we have neither the ability to do nor access to.
It seems to me that this argument is perhaps due, at least in part, to our own bias. What I mean is that, at least for me, when I have a raid member die just before my heal lands it is easy to notice, extremely frustrating and I tend to remember it well. It is much harder to notice if your raid suffers deaths because your heals are not large enough. A deficiency in heal size would more likely manifest itself as slowly decreasing HP levels throughout your raid â€“ if each heal you cast is a couple hundred HP smaller than it needs to be you probably wonâ€™t notice any problems at first, but after a minute or two those couple hundred HP deficits begin to add up and it appears that the raid damage is just overwhelming. Or if you are tank healing, it is easy to say that a tank death was due to a bad spike of damage, but itâ€™s not always easy to notice that if your heal 5 seconds before the tank died had actually been slightly larger it would have saved him from that spike.
Another argument that is often seen is,
Which is of questionable validity. Hard mode fights are more difficult all around and should theoretically require more of everything â€“ spell power, haste, crit, longevity, reaction speed, better decision making, etc. There is nothing inherently unique about haste in regards to hard modes.
Hard modes require lots of haste.