If you crank your bars far enough they will hit or ride to close to the top bump stops causing a not so smooth ride. That's why some trim them.
Now if you want to make a low rider out of it, crank the bars down and trim the lower bump stops.
I have cranked my bars to raised the front end about 1" to 1 1/2" from stock to level it out and did not trim the stops. It's the best riding rig on the road. Smooth as silk.
