Today, movies are printed and the prints are sent via land, sea, and air to the various theater chains. Even though security is tight, piracy of the print to be shown does happen. Prints for a typical movie are expensive. Prints also show wear and tear. Prints get scratched and cinched.
Prints break and have to be spliced back together while the audience sits and waits.
Sometimes print reels inadvertently get shown out of sequence. Also, when switching from one reel to another, the film might be projected out of focus, sometimes for only a short time, sometimes for the length of the whole reel. In the near future, a whole new way of delivering movies will evolve. This is not desirable, since film in the U.S. is shot and projected at 24 fps. Not a very good idea.