Another thing to remember is that you'll want several options to send the pass to. If your ideal recipient goes down, the passer doesn't have a whole lot to do. (Pass attack boosts and defense drops to a Giratina? Maybe not.) Alternatively, the enemy may have a Pokemon out that can destroy your pass target on the switch. Say, Groudon against your Dialga.
Example: On my RU team, I usually pass from Ninjask to Relicanth, but if the enemy has an electric or grass type out, that's suicide. So I have Camerupt ready to take that kind of hit.