One thing apparently is that it guarantees they won't rat, because to get into the club they have to participate in all kinds of sick shit knowing it is filmed and photographed. So they know if they ever go against the group there's a world of incriminating material ready to rain down on them. Of course the alternative is they're lured into doing this sick shit and then blackmailed and controlled knowing that this material is hanging over them (Epstein was rumoured to be doing this)
But if you read about things like the Dutroux
ring and all the crazy shit that was happening to kids at these kind of parties, attended by European elites, clearly there are plenty who are just pure evil and get sadistic pleasure out of it
Here is a long but detailed documentary on the Dutroux case, which includes details on the level of people involved and how insane the coverup was