You need to ensure that everything below decks is in its rightful place / state. We need to avoid having heavy objects flying around the cabin, doors banging, water rushing through open hatches etc.

You want to make sure that before you set sail the deck is clear, all lines are in their place, no ‘things’ are lying around the place, that the crew is briefed etc. so there is no confusion as you leave your berth, mooring, anchor and all goes smoothly as you set sail

Checklist for going on a charter yacht, provided by @CassandravillE