Something I'd like to add, if I may, is a rule of thumb I try to follow while controlling. To me it seems the only time a controller should be at 100% power is when every other member of the group is as well. I always found it more important for everyone else to be topped off more than the controller. I'm not saying a controller should always empty his bar, though. After all, there are times someone may get drained by an Eye Drone or something, and if you don't have power to give then they won't to heal, damage, etc.