Okay, so the title might sound a wee bit hostile (Ive discovered recently that my stuff is the stuff I do from the get go and if I think about it too much.....) but this is one of those questions I have often asked.
Years ago I was made aware of a guild that was all Druids and that the participants of this guild were Druid "purists". Now, what is purism in WOW? The variance here depending on the person, I imagine, would be gigantic, but from what I remember the guild was very into RP and stuck to what ever Druid lore is, and never used mounts, only using travel and flight form.
Kind of cool, actually.
My contribution to purism in WOW takes shape with my healers. I no longer dual spec my heals. There are a few toons that have a DPS spec that I will change in to from time to time, but that is more an aspect of that toons personality as I have come to know them, not a mechanic to make use of in the game.
Managing a second spec on a toon used to be a lot harder as there was no gear set option, it could never be done on the fly and talents weren't saved (or were they? Lord I am getting old!!!). Modern spec switching woes these days more or less amount to being able to play said second spec effectively. This, my dear friends, is one my foundation reasons for being an altaholic!
There are six healing spec's available in WOW. All of them have abilites that are offensive, but are not very powerful. Anyone of them can kill a mob, but it takes like 8 years, and one must be very aware of mana, as you can blow out all of your mana trying to kill something and then have nothing left to heal yourself! That kind of thing happend on my Monk. Monk abilities seem to have a GIGANTIC mana cost.
Druids have an ability that converts Spirit into Agility while in Bear/Cat form. You'd think that would make life easier playing Resto all the time, but no so much. Throwing down and Efflorescense to stand in while you kill a mob is helpful, but you can start attacking something and go fold laundry and come back before you will actually kill it.
To date the best "travelling" healing spec is Disc. I has to have the highest DPS output and you heal while you do damage.
All of this being said I am not sure how this could change. The balancing that would need to happen if heals were to be able to dps, like, well, a dps class would likely throw things all out of wack, but after all, these are just my rants, raves, and yelps.
Thanks for comming!
All the best!