anyway, i personally would use a healer to heal, casting defensive spells or curing etc... thus feeling the need for some sort of tank.
If I was RPing a 'true' healer, I probably would only use it to heal/protect, along with using Absorb Health, quite possibly the best spell in the game.
Also, absorb can be useful in a fight... restoration is not completely helpless in a fight... (i had a restorationalist once... though she did wear heavy armor X<)
As I said before, Absorb is beast. It takes away the opponents health and gives it to you, thats just fantastic.