A version control repository IS a backup. But you really should back up the respository.
As always, back ups should be to a different device than the main file: a hard drive on another computer, CD, thumb drive, whatever. A backup on the same disk drive is worth something, but the most likely reason to need a backup is because the hard drive failed.
For real safety, keep the backup in a separate location from the original. Like I used to work for a small company, and I took backups home with me, so if the building burned down, we still had our backups. For my home stuff, I sometimes take a backup to work and stuff it in a drawer in my desk. 'Can't imagine the company minds me using up a few square inches of desk space.
Personally, I'm bad in that I only make my backups once every few months. Backup schedule should depend on how frequently your data changes and how important it is.