Literally not a thing.
The cool part is many catamarans are captained. You are paying for someone who can guide you in where to do, when to go, the best places to see and things to do.
A captain is also responsible for safety on the catamaran and will allow you to do as little or as much a you like.
Want to sail? Great. Want to lay in the hammock and read books? Great!
They normally will stock the boat before you get there based on your preferences for food and drink, and pre-plan any special events like diving, snorkeling, windsurfing or visits to special places.
Fly or dive in - get on the boat and go. How easy can that be?