If an engine is overfilled with oil, the cranks can splash too much oil around the engine. This can lead to too much oil on the bores, which can cause smoking and at worst break rings. I have seen a Honda XL 350 where the owner had changed the oil, except that having previously only owned two strokes, he didn't realise that you had to drain the old oil out first. So it was well over filled, and was smoking badly as well as tending to weep a bit out of the joints. Once it was drained and refilled with the right amount it all came right again with no damage.
John