Healing Strategies:

Over-healing:
Consider the following: you have a mana pool of 100 and you can cast a heal that heals for 100, with a cost of 10. If you play it right you can heal a total of 10 times for 100 hp each time. In total that a possible 1000 points of health that you can restore to any given party member. So I ask you: Would you use your heal if it only restored 10 points of health?

No, you wouldn't.

This is where over-healing comes into play. In the ideal world every heal that you toss out should heal its full amount, if not close to it. Each you that heals beyond 100% is waste of mana. This aspect is particularly important to CNJs as they have no true form of mana regeneration at low levels.