training them for sports specific function makes sense...I don't know if it does from a pure bodybuilding standpoint. I've never worried to much about training a stabilizer...I will take a few sessions to get "used' to doing a movement before I incorperate it into my routine so maybe I'm getting my stabilizers ready and just never thought about it. I just think if you walk around all day avoiding a machine because you're afraid you're not going to hit your stabilizers your taking it too far.
Everyone benefits from stabilizer training, from a pure bodybuilding standpoint, it would be much less for bodybuilding than it would be from athletics, since bodybuilding is not a performance sport (it's not a sport at all

) meaning speed, agility, conditioning it's not needed as much as say a football player, baseball, soccer,etc,etc but it is needed.
Machines are great for bodybuilding because it the working muscle directly, anotherwords not many other muscles are involved in the movement to provide stability. As an example, and i have used this analogy before, just because a guy has huge muscles doesn't mean he can throw a baseball 100mph or run a 4.4 40, he might be able to overhead press 315lbs but there's also a good chance he can tear a rotator cuff throwing a 6oz baseball, see my point?