The companies that make the dynamic balancing equiptment usually give talks at EAA and Sun N Fun, etc.
They put a marker, like a piece of reflective tape on one blade, then run the engine and shoot a strobe light at the prop arc, and have a sensor like a small plunger that measures the vibration and the strobe shows where the heavy point of the arc occurs. Then put on a temporary stick on weight and run it again, perhaps taking several times to get it right. Then bolt on the permanent weight, like a washer under a spinner screw.
Note that it may be rough at more than one rpm and smooth in between. If you have one blade tracking diferent than the others, it can be rough.
There's no downside to proper balance; not like getting a hight rev cam or a big carb that may hurt low rpm power and starting. Balance helps everywhere.
It usually only cost about $150 and takes and hour or two for most planes( Spruce Goose may be a little extra).
Money well spent for mostany plane and just static balance does not do it all.
I rode in a tri motor at Oshkosh and it really shook so much it was a bit scary. Hope they do it over the winter.