Crossfadiing of audio edits is essential to arriving at a seamless result when joining tracks together. If it isn't done, the edits will instantly stand out and jar the listener away from their suspension of disbelief, which is the very last thing you want to happen in something that is supposed to be an uninterrupted movie experience.

Edit points must also be chosen very carefully, particularly when there is music involved. Trust me, I wrestle with this kind of thing all the time . . .