You have to use Source Control for these reasons
1) You can rollback to any version
2) Different developers can work on the same files
3) All developers, will have access to the same code base
4) You can track changes
5) You can rollback changes that don't work
6) Source control is the basis of continuous integration and helps massively with TDD
7) If you don't use source control, you will slowly go mad as files get lost/overwritten and nothing works as it should
VSS is not the worst SCC application, I used it for years and grew to hate it, but it does work, is simple, and many people know it.