Having a court order means having the right to go back to the court to let it know that other party is not abiding by the terms of their arrangement.
While it may be extreme, it is sometimes necessary to call the police to enforce a child custody agreement. The police will only enforce the agreement, however, if it is a court order. For example, if one parent is refusing to transfer the child to the other, they can go to the police to enforce the court order immediately.