To avoid confusion in conversation when referring to spending the night with a girl/guy. The term "sleeping with" is often used to refer to having sex. However, if you just slept over in the same bed without sexual acts, you were "asleeping with".

when you're hungover as shit after a spending a night drunk as a skunk

What you are doing when you leave your msn on overnight. This term is used primarily in msn conversations or away messages. You are away and asleep. You are asleeping.

When someone is in a deep sleep