A term used to say that instead of intimacy in a relationship, you can get the sex for free( via slut, whore, prostitute, etc.) Also in the statement, " Why buy the cow, when you can get the milk for free?"
Caboose: My dad always said " Why buy the cow, when you can get the milk for free?"
Church: Hey Rookie. Did you just call my girfriend a cow?
Tucker: No dude, I think he called her a slut.