I was gonna address this in my warrior guide which I’m holding off on until server launch, but I might as well do it now since this is a common discussion. For a bit of background information, I’ve maintanked/offtanked all the dungeons up to the last released raid, as well as been in numerous raid groups with other classes tanking, so I have a bit of experience, and not from just theorycrafting. Scroll down for the tl;dr version below if you want a quick answer.
Although this topic is about main tanks, I feel it’s relevent to talk about the 2 “Tank” roles, since the ability to off tank should be considered as advantage to main tanks. One is the “Main Tank” and the other is the “Off Tank”. The Main Tank is the player who will be tanking the boss, and holding aggro until it dies. The Off Tank has many different responsibilities. The main thing is to handle boss summons (adds). Other responsibilities includes luring when needed, and holding the boss while the priests/sorcerer’s are ressurecting the Main Tank. (Note that in certain situations, such as some dungeons, a party is capable of taking down adds. Hence, an Off Tank isn’t necessary. However, they become more and more important, the higher you go in difficulty)
