It’s a bargaining chip that isn’t counted against the salary cap.
I think the player options to Dylan, Moses, Matto and Penisini simply does two things:-
1. Let's them know that the club values them long term, and
2. By mere fact that they have an option at the end of their contract term, brings them the table to talk about it.
What clubs like us a Storm, Raiders, Titans, Manly have done is gambled that their players will remain an elite and in demand sportsman for at least that part of their careers.
St George have a 7 called Hamish Stewart and whilst he has not played NRL as yet, is under contract until 2026 with a PO. I wonder what they were thinking ? My guess is that they wanted Stewart to sign until 2027+ however the manager said no. So the PO was offered as a sign of confidence and unanimity as they face new teams entering the NRL around that time.