When you become too lazy to finish a sentence or you just realize you dont want to finish the sentence.
Also used when a more important matter must be expressed. substitutes points of ill importance.
"Oh I was out with the guys.
girlfirned: What did you do?
"Oh you know we went to the bar and ..
you know the bar and shit. Hey how about that Sea Biscuit movie! wanna go see that?"
Also used to make things that aren't really as interesting as you had thought in your head seem cooler.
"yeah then we played. . .and shit. ."
"yoo! guess what! i just saw this girl! and she was hot and shitt"