ORIGINAL: flycatch
A rotating mass that is out of balance will create vibration. Vibration over time will cause things to become loose. Do your self a favor and balance your propellors.
In that case, you'd better throw away the piston in your engine.
Did you know that if you put an unbalanced prop on your engine with the heavy side opposite to the piston direction that you will actually REDUCE vibration?
The AMA did a series of tests on this 2 years ago, and their findings were that for a sport engine, balancing the prop (Except in extreme cases) was totally unnecessary.