Note: This post applies to all classes except healers. Healers should stay on MT.
I hate the method of targeting through the MT. It works and its simple, its also lazy, and like most things lazy, its not the right way. I will explain why. When youre fighting one MOB, it doesnt really matter, but as soon as you draw a group of MOBs then its a problem. Everyone in the group should always be focused on the same mob as the MT, however sometimes the MT needs to switch to a MOB that is smacking around the healer, or the over zealous scout/mage to taunt the mob off and get it back on him. While this is happening you dont want to switch with the MT, he isnt trying to do a lot of damage, just get agro back, which usually the MT has taunts that can do that. You should still be focusing on the original mob to kill it, and if the MT knows what he is doing, he will come back to the original MOB once he gets aggro back from the MOB with a wondering eye. Now say you are targeting the MT and assisting through him, you are about to unload one of your better attacks, and just before it goes off, the MT switches to another MOB to taunt off the healer, your super_attack01 goes off hitting this other MOB, so now the MT has to taunt the MOB off the healer then off of you, which will be hard because you just laid into the MOB big time with your attack. Well you have armor thats about as tough as a wet paper bag, the MOB beats you like a red headed step child and the healer mana burns to keep you alive. Guess what happens now, the MOB goes back to the healer because all the heals she just sent off to keep you from dying, in the mean time the original MOB is smacking the crap out of the MT and no one is touching it because they all want to assist the lazy way. The healer runs out of power trying to keep himself, you and the MT alive through all of this. which now means that everyone dies, because you couldnt make an assist macro.
Dont get me wrong, this is a way extreme example, but it makes my point, and if you toss in a chanter in there that is mezzing MOBS and you assist through the tank, as he TABS through to the next MOB he wants to kill, you will break every mezz, effectively killing the enchanter in the process (which isnt a bad thing in my opinion, but still).
Make an assist Hotkey, every time the MT moves on to a new MOB just push the key once. this is what I do when I join a group.
"Hello everyone, how are you doing?"
"Who do I Assist?"
then i edit my assist key. the commmand looks like this
/assist meatshield_01
it takes two seconds and you never have to worry about it again until the MT changes.