I got in the prop balancing habit from boating. Having an off balance metal prop spinning at 25K RPMS on the end of a flexible shaft isn't a good thing. When I started flying I just naturally did the same for plane props. However, I'm significantly less fussy with my plane props. Most of the time I just check to confirm that it's sorta close. Sorta close is never good enough for the boat props.

If you want to determine the effects of an off balance prop, chuck one in a drill and see what the vibrations are like. Note to any Darwin award candidates, don't blame me if you mess up this experiment.