It's almost impossible to polish enough off a crankshaft by hand to make a noticeable change in the clearance. I usually use something in the range of 320 to 400 grit cloth-backed emery cloth, 1" wide and about 2 feet long, using a shoeshine type motion and rotating the crankshaft so the polishing is done evenly all the way around. This simply knocks down any high spots that might damage a new bearing.

New insert bearings have a very thin top layer of pure tin which allows the bearing to "wear in" to the surface contour of the crankshaft very quickly. Hand-polishing the shaft prevents any roughness that might be present from eroding the wear-in layer.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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