It's my understanding that Bp's (and many snakes) don't need them. They get all the vitamins they really need from their food. In some cases vitamins are bad, I can't remember what ones do what in excess but unless your vet recommends them I would advise against them. They can be used in several circumstances but those are normally prescribed by the vet as treatments or a nutritional boost while healing.

I know some block the processing of calcium, some can do damage to their internal organs.