This is another old school deal that will have people both ways fight this tooth and nail they are right. But no hard core medical proof either way.
People were a belt for different reasons.
The only definite proof of help it does, is people watch there form better when they ware a belt causing less people to get hurt.
Oh I will get flamed by the "It locks your core" and stuff like that but there is nothing no-ware proving this is a fact and not just old school theory or research done by a special intrest group that will benofit by the results they provide.
So bottom line you want to ware one do it. You want to build up your core don't.