When you periodically update a file, ocassionally you find that -- somewhere along the line -- you broke something. It's at these moments that you wish you could go back to previous versions of said file, looking for where you (or someone else) made the mistake. That's what revision control systems are for. You archive a file into a repository of some sort, and then check-out/revise/check-in the file as necessary.
The alternative is to repeatedly gzip and store your files, and hope that you don't get confused or take up too much storage space.
- GNU Arch
- Subversion (svn)
- Bazaar (bzr)
- SCCS or its GNU clone cssc