Wiki is your friend:
"Most locking tremolo systems currently in production are "floating" bridges, a concept first popularized by Steve Vai. Vai, wanting the ability to both lower and raise the pitch (by pulling on the bar) had a carved "lion's claw" cavity behind the bridge to allow the bridge to be raised further than normal. Guitar manufacturers prefer this type of configuration because mounting the bridge in this way is both easier for builders (because the neck does not need to be mounted on an angle when mounted within the body of the guitar) and because it increases functionality."