Though the strategy of running back handcuffs for fantasy football is as old as stadium dirt, I personally have never used that strategy.
I would rather draft a starting RB on another team than a backup on the same team. The reason being that another team's starting RB is typically more talented than the injured RB's backup.
For example, I would rather take a starter like Mark Ingram or Donald Brown than Ray Rice's projected backup, Anthony Allen.
As a matter of fact, I would more often take a RBBC player, like David Wilson or C.J. Spiller, than LeSean McCoy's projected backup, Dion Lewis.
That said, there are a few situations where taking a handcuff makes absolute sense.