Response to Maelwys..

Yes and no. As someone whose healed and tanked for a while I'd say that it really boils down to the encounter in question. It's not always necessary to keep the tank topped up at max health especially if it's going to result in unnecessary over healing (Where avoidable of course).

More often than not healers would only overheal during periods of expected high damage and then go back to 'normal' healing the rest of the time. You also have to take into account class mechanics i.e. some classes being pre-disposed to reactive healing or overhealing.