One problem with overfilling (if overfilled enough) is that it can damage both crankshaft seals. The front seal isn't too bad, but a rear main seal ain't cheap to replace.
One of our dealers REALLY overfilled the crankcase on our C230, and it blew both seals. Replaced under warranty, but it was the last oil change not done by me.
1998 C230 "Black Betty"