If the same people clear out as clear in then there's no big difference. But if guests plan on returning via a ferry then it is a problem, as they have to go to the C&I office with the skipper with their ferry/plane tickets and be taken off the boat papers. If you clear in with x number of persons on board and clear out with x-3 people, C&I will demand proof of where those 3 people are. The captain is responsible for all crew, so if things go really badly then you will be denied permission to leave until you've furnished proof.