Sorry, in advance, if this has been discussed previously.
Also, in advance, I do not want a genuine fight to break out over this. I am more interested in hearing opposing viewpoints--the reason being, I am considering changing my opinion (outwardly, at least). :P
The discussion started over the mention of druids, shaman, and paladins, wearing armor with good stats and +healing, that was less than their maximum armor proficiency. (That is, druid wearing cloth; shaman wearing cloth or leather; paladin wearing cloth, leather, or mail; etc.) In my opinion, this is totally acceptable; while I think that one should try to find gear of your expected armor proficiency, I also see no problem upgrading to a piece that is below that maximum. There are a few times I have seen this happen, especially in gearing up new 70s in Kara and heroics--yes, there are good pieces out there for you, with a higher armor value, but it could take you a long time to get it and we need your healing to be better NOW!
(Side note: This would be invalid to me, however, in the following scenario: Cloth healing gear drops; three healers need it; one is a priest, one a druid, one a paladin; if the cloth-only wearer needs it, then IMO, the druid and paladin should in no instance be rolling, because they can get better, but the priest cannot.)
My aunt--the woman with whom I was arguing--does not agree, however. She says that, considering that there are good leather/mail/plate healing pieces, there should in no occasion whatsoever, be a druid/shaman/paladin wearing cloth/leather/mail gear. Her main argument is that they do not have the aggro management capabilities of a priest, and therefore need all the armor they can get--she argues their main selling point, as a healer, is the increased armor, and therefore, increased chance of surviving loose aggro.
This is a valid point, in my opinion, but once you hit Kara and onwards, I think it becomes increasingly invalid. Why? Because in Kara and beyond, if you have a mob on your healer--especially, a boss--the shit has pretty much hit the fan, regardless; a mob will tear through a healer pretty quickly--whether it tears through the priest in one hit, or the paladin in five, is usually irrelevant (in my experience). Not to mention the fact that if a healer catches aggro in a raid, it is 80% of the time because the tank is dead, not because the tank failed to hold aggro. And while there are fights with random aggro/attacks, or AoE attacks, most of these are magic (please correct me if I am wrong--it has been a while since I raided!) and therefore armor does not much help.
I would love to hear more opinions on this, however! I'll be eagerly awaiting e-mail notifications. :P