Well, a prop balancer allows you find out if one of your prop blades is heavier than the other. Sometimes the Hub can be heavier as well. To correct this weight variation you can add weight to the lighter side of the prop using different mediums such as spray adheasive, CA, tape or clear cote finish. Some people like to sand the prop blades to remove weight, but that can be adverse and change the airfoil shape of the prop.

A perfectly balanced prop should be able to remain stationary in any orientation.