How big is the prop? If your prop is in the 5 - 9 inch range, forget it altogether (unless you are running a racing engine), if it is in the 9 - 10 - 11 inch diameter range with a sport engine, then balancing isn't very important but it can be an interesting exercise just for the fun of doing it. If is 12 - 13" then a balancing is a good idea but the world won't end if you forget to do it. If it is 14" or more, then you had better balance it.