The three blade props are usually for that nice, scale warbird that you want to look cool sitting in the pits.

As far as not re-balancing after a prop strike, the answer we are supposed to give is that a prop should be balanced whenever it comes in contact with the ground. The reason I suggest MA nylon props for learning is that they are much more forgiving of these frequent little mishaps, and you can usually get away with firing the engine back up and going again, but you are never supposed to admit that you do it. Oh yeah, and I use after run oil after EVERY day at the field... I promise