A flip could be used to get over a larger gap then you can jump, (as said above by Thomas,) for getting yourself right side up if you'd fallen backwards from somewhere, and flipping over a spiked-topped gate you cannot normally get a good vert jump over. Those three situations would be the most "common."
If the rest of you wish to talk about the practicality of parkour/freerunning, (or whatever it is you are discussing?) please start a new topic.