1) You
don't care, or you
don't know what to do.
2) When you really do care about something but you
don't want to hurt anyone's feelings, or make them mad or something.
Boy: "So where do you want to eat?"
Girl: (really wants to eat at "McDonald's") "It doesn't matter".
Boy: "Alright, LET'S GO TO '
BURGER KING'!!!!"
Girl: (I was hoping that we could go to "McDonald's", but...ah, it's fine)