@Sophistifunk @halfpint
never in my life have I disconnected a battery to do work on a car, unless it was to replace the battery. this includes "serious" work like replacing the rod bearings.
no "damage" comes from being unplugged, but recent experience with a recently built model taught me that it's annoying.
maybe it's common practice in your part of the world. but I've never seen it or heard of it