The use for them is to store your cvar values when a server changes the cvar values of your config when disallowed values are found.
They might be useful
When a server finds disallowed values in your config you will load the map twice when you connect to the server. When this happens, you should look at the newest cvar_backup file and change the cvar values of the cvars listed in the file to match the allowed values.
If you have your config in your etconfig.cfg in your profile (why would anyone?) instead of an autoexec.cfg and corresponding .cfg files, the cvar backups are useful if some war server changes your cvars and you want your old values back when you play on a pub.
yes, delete them
its something like a cfg backup ( or not?)
They might be useful
When a server finds disallowed values in your config you will load the map twice when you connect to the server. When this happens, you should look at the newest cvar_backup file and change the cvar values of the cvars listed in the file to match the allowed values.
If you have your config in your etconfig.cfg in your profile (why would anyone?) instead of an autoexec.cfg and corresponding .cfg files, the cvar backups are useful if some war server changes your cvars and you want your old values back when you play on a pub.
Err.. Shortly, you don't really need them.