This allows different customers to share the same resource at the same time. There are three models you can use: either sharing is disabled (use in most cases), allowed (it's up to the customer to decide whether other customers can share the resource), or always possible (this forces all clients to share the resource with the others).
Forced sharing is a good idea for resources such as dormitories and optional sharing can be used e.g. for big yachts in a yacht club or basketball courts where a single customer can either rent the whole resource or share it with other members.