Never ballanced a prop? and no problems from it? You got very lucky.

APC Grey props rearely need any ballance adjustment. Every other brand and type prop I have tried... almost always is out of ballance.

A slightly imballanced prop puts an added vibration load on the aircraft if nothing else. That can lead to glue joint fialures. More imballanced and you get fuel foaming problems, which can lead to unexplained dead-sticks anywhere from 7/8 full tank to 1/3 tank. If the imballance is severe enough it will just rip the engine off the firewall.

One method for ballancing is to paint the light tip. First paint both tips some bright color to help make the prop arc visible. When that drys, balance check and add another coat to the front of the heavy blade (just at the tip, not the whole blade)

Another is to lightly sand the front of the heavy blade. Avoid sanding the back (flat) side as that has a larger chance of changing the pitch in the area sanded.

You can lightly sand the leading edge to remove mold flashing. Its a bad idea to sand the trailing edge, especially with APC grey props. (yes those are the ones that are the sharpest at the TE...) The trailing edge of the APC is sharp for a purpose. It helps reduce the load of the prop on the engine and helps reduce prop noise.