An important part of story telling is transitions from one scene to another. The same holds true for film making. Well thought out transitions can evoke emotions and convey a message. a bunch of fast flashes can create confusion and possibly a sense of mystery while slower scene transitions can create a more peaceful flow.
Scott Pilgrim vs The World contains many uses of creative transitions. Check out this breakdown of some of the transitions in Scott Pilgrim vs The World and why they work so well: