Hey, another question about props.... How important is it to balance propellers? And is this primarily done with wooden ones, or do all propellers require it?

Another question, I have a Hobbistar 60, and in the manufacturers documentation it tells where the center of gravity should be to balance it, but I also have an older Global Cessna, and am not sure where to balance this one. My question is, is there a general rule of thumb for balancing planes? Or is each one pretty unique in that?

Thanks, Caleb