MPC green has literally no benefit! I can't think of any other benefit other than your boarding priority and your very slim chance of op-up on a fully booked flight. Be a silver tier or higher, then you'd start enjoying some benefits such as lounge invitation, priority check in (in J counter), and priority baggage tag.

An exception is if you're originated at HKG. I think they have a designated check in counter for all MPC members, including green. CMIIW though, it's been quite sometime since I have not travel to/from HKG other than for transitting.