There are several video players for Linux, Xine, Kaffeine, Mplayer etc. They are good, but VLC can play many files and dvds (even encrypted) that other video players cannot. It can also
- receive video streams and save them to disk
- send video streams
- and backup/rip video content for dvd to disk
- convert video to mp4
VLC bypasses copy protection, since it plays the content in order to encode it.