If the oil pan is overfilled to excess the oil in the pan can come into contact with the rotating crankshaft. This can casue oil frothing which is bad. The slight overfill of about 1/2 quart doesn't pose a threat of frothing.

I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson