Handcuffs don't interest me too much unless the backup is a guy like DeShaun Foster who (1) will be getting significant time anyway and (2) would be THE MAN were something to happen to Stephen Davis. Unless both of these conditions are met, I say handcuffs are a waste of roster room.
So Priest Holmes gets hurt and you don't have Larry Johnson -- what do you do? Yeah, maybe think about picking him up. Maybe. Or you could take a shot on another back with no NFL experience to speak of. But if you've drafted well, you already have a backup to your two starting RB slots -- like a Lee Suggs, Tyrone Wheatley, Charlie Garner, a back you can get LATE in a draft. Or a DeShaun Foster.
Why are we so intersted in an elite RB's backup when we will have bonified NFL starters to plug into our lineup if that stud RB gets hurt?