Over filling by a small amount up to maybe 150ml shouldn't cause any issues, in fact, I've seen many engines over filled by at least 1500ml that were running perfectly well.
Over filling of oil, in some cases can cause excess internal pressure which would need to escape from the weakest points. These being, seals and cam cover gasket, the latter being most common and worst case scenario would be a complete engine lock that can destroy many internal parts.