The difference between a good WHM and a bad WHM is whether the party lives. Healing is the WHM's job. Being good at what you're designed to do is pleasant, but not notable.

The difference between good and great is what the WHM is doing above and beyond the core role. If you can throw DPS and crowd control while seeing to your healing role, definitely do. If you find you're out of mp or can't hold it together, scale back, gear up, practice a little harder. Keep people alive first. Don't lose sight of what you're there for.