I've been toying with driving from the healer in PvE situations(not instances), and it works well when questing, but when doing instances you want the extra control. Reason being that positioning is so important as you only block and parry attacks from mobs in front of you, dodging I think works in a 360 way(but not sure). So by using IWT you might end up with having your back to most the mobs and healing becomes really hard.