I was wondering about this also.
The "touched-up" spot tends to be either concave (paiting over a chipped paint and/or primer) or convex (excess touch-up paint on a small chip/scratch). Should the tiny chip be filled-in with some sort of bondo or something to bring a smoother surface then touched up? Once dry, should excess touch-up paint "bumps" be buffed or polished down with one of those tiny dremel buffers/polishers to make it a smooth surface? Just looking for suggestions if anyone has obtained good results from their touch-up techniques.