A downside is that every time a watch is overhauled, there is a small risk of inadvertent cosmetic damage. There are tales of woe of watches returned with new dings or scratches too deep to be polished out, scratch marks on the dial or hands, etc. Watchmakers however competent and careful are only human & accidents do happen when doing all that delicate work. When you think about it, the typical cost of an overhaul is really not that much, bearing in mind the knowledge, expertise, skill, care and attention required.
Personally I allow 10 years between routine overhauls, or sooner if the performance deteriorates beyond what is reasonably acceptable.