Infraction: 1. All posters are to make an effort to communicate clearly.
Message to User:
One sentence per line.
That's what you've done here.
Why, I have no idea.
Depends on your point of view I suppose.
On one end of the spectrum, it's only "really needed" if you wouldn't have killed a boss without it, but would if you did flask.
On the other side, it's really needed if it causes you to do any additional DPS which helps your guild move through the instance better, faster, harder.
Most of us are somewhere in the middle; here at EJ, I imagine we are skewed more towards the latter than the former.
My guild is still moving through progression content, so I personally always use one. It helps that they are on the same timer as poisons now, so I just do it all during the required hourly rebuff.