It's not all that it's cracked up to be...
If you're using Disc-Disc-Tape backups, your staging disc area needs to be FAST. I've found (the hard way) that disc systems aren't anywhere near as fast as they claim to be.
If you're doing snapshots, then backing up the snapshots to tape, you'll be hammering the live discs (and hurting performance) whilst you backup the snapshot.