i think he is talking about when the blades are level and u flip it 180 degs and it flips back ,with my carbon props i sand off some of the heavy side of the hub ,rather than adding to the lite side .
being so close to the center ,it is hard to tell how much it will affect the running of the engine
after spending 30 min balancing a prop a greasy fingerprint will throw it out of balance so go figure
many a race has been won with a prop that was damaged half way through the flight ,and more than one speed event has been won with a prop that had the tips shortend with a pair of side cutters and rounded off on the pavement .that said, the better the balance the better your engine will run in the long run.