My point, was that HoTs not being fire-and-forget is flawed, because (in most fights) the only people you have 100% uptime for your HoTs is tanks.
I can just off the top of my head think of several cases where your statement is not entirely valid. True many fights you don't have to focus on ten or more targets, but in MOST fights, you are going to be healing more than just the MT/OT.
First let me preface this by stating I have not yet configured Grid properly, so am not using it in raids. I see a couple benefits to grid knowing who is still hotted up. One obviously is effective healing, but secondly, this can be better than having a second innervate or hundreds more MP5.
I say this because contrary to the quoted comment above, there actually are several encounters where you want to have practically 100% uptime on hots to a very large number of people.
The most obvious example is Sapphiron. As a resto druid, I can completely negate the periodic frost damage ticks for an entire 10 man raid by maintaining rejuv on every target. So that is one example that explains effective healing.
Secondly, on the mana gain side, I currently use x-perl, so I only can easily only track my hots on my target and focus, which means I am most likely wasting a TON of mana, refreshing hots on targets that already have hots with half duration remaining or more, simply because it's not that easy to mentally track who has what hot, on a large pool of raid members.
There are many other examples where phases of boss fights this would be a great help, such as pre-hots for Malygos for the cyclone or whatever it's called. Making sure your assigned targets have hots up before the healing window opens on Loetheb, decimate on Gluth.
Heck even wildgrowth in it's current state, if you have a bunch of people at low health, and wildgrowth one player, you don't necessarily know all 4 of the other players that received the hot, so seeing this instantly, can assist you if you need to cast a second one, to avoid re-casting it on a target that currently has it. Of course, this all changes post 3.08, but still it's just another example.
In any case, I think my point is fairly clear. Knowing all this information not only will increase your effective healing, it will save you a boat load of mana, since we still are one of the best raid heal classes in the game, and an addon like grid seems to be a great way to maximize this roll.