Without a file-system data and documents would be random and extremely hard to find. Unix files systems (XIS, NS, E2FS, Min ix...) all have file level access control (owner, group, world) and allow very fine control over user rights. In addition, the way they handle files allows them to be fairly immune to disk/file fragmentation. Unix file-systems are built for multiple concurrent users so they must be more robust than say MS-DOS.
