It's pretty much useless... Restore to backup does not restore music on same computer. Have to install apps again... have to re-jailbreak (did it with Greenpois0n this time).
It's not entirely useless: a restore from backup is the only way to restore application data. The backup itself is not meant to replicate data that should already be stored in iTunes, like music, videos, podcasts, photos, etc.
After all, backing up such data would lead to unnecessarily large backup files and back-up times, and just reproduce data that is already stored on your computer, and backed-up elsewhere.