I wonder what the risks are, of using an electric polishing/buffing machine? Can you over-polish and cause "brassing" on a gold watch case?

When a "brassing" spot appears, is this most likely due to wear and tear, over time, with the age of the watch; or could it have been caused by over-polishing that spot with an electric polishing/buffing machine?

Is it safer to polish gold watch cases by hand, or is it okay to use the electric machine?