In exchange for having taken the time to understand and declare exactly what you depend on to be productive (and nothing else), you get to start ~productively-fresh instead of living in a cargo cult of whatever unexamined arbitrary state and executables were present at your last backup.
It also means you aren't completely out of luck if you get lazy and don't test your backups for 6 months only to find out they stopped working after you ran some `blah blah update/upgrade` command.
