1. Does not have anything more inteligent to say.
2. does not want to go along with the conversation or the stream of thought.
3. It is tired of the other person and just wants the recepient to shut up.
4. A simple way of ending a conversation.
Recepient: alright, I had a long day, I had to work extra hours in this project, and the people in my office are driving me insane.