I didnt say anything about you being vague, no point in bringing Steel into this.
Most fights with AE DoTs, there will generally be some group healing going on. So, if youre gonna be hit by these, whats the point of using purify body? As for root/snare... I cant think of a time outside of maybe Torment, Enforcer building in SK, librarians in SE, uh... those are it to my knowledge on pulling. Even then, monks get Freedom of Body and generally resist magic based snares/roots quite easily, and either way it doesnt = death. For Fear/Mez pulling, using the immune stance is easy enough and drains stamina very slowly. For single target DoTs while pulling, I cant think of a single one that is deadly enough to kill a raid buffed monk before the pull is over, including Sunderdrakes, where the pulling is minimal enough to get back to a bard with almost no problem.
Even if a failed FD doesnt kill you, it certainly has the potential to really fuck a pull youre working on, especially if theyre casters. Itd be nice for the more difficult splits in the game at the low to mid parts of raiding (NDHK Yziar/TR, some SE pulls, Firkaal, lots of trash in Torment/Air etc) where you can bank on having a get out of shit free card in this AA. I think it would be way more useful than Purify Body. Just because you use it 2-3 times on a raid, it doesnt mean its necessary that you do.