Having a personal backup saves you the embarrassment of groveling to the system administrator to see if he might be able to find your files within last night’s system backup.
Of course, you may want to make a quick backup of the bad code first. Hopefully, you can use something and not have to entirely recreate the work you lost by reverting to the backup version. Still, this is a better option than being under stress to correct an existing problem on the development server (by the way, you would never develop on the production server, right?).