There are so many benefits to having members...
They become walking talking advocates for your business. It's far better than any 5-star review posted online.
I've had members come back with their friends on multiple occasions to show it off to them and pay for additional sessions.
Members can fill out your off-peak hours (I restrict my members from coming during the day on weekends).
Some members will sign up and rarely use it, that's free money. To be fair you do get the opposite as well, some members will try to find ways to bend the rules to get more than they're allocated.
It's a good topic to bring up when a customer asks how much the equipment cost because they want to get one at home. Suggesting they sign up for a membership is a great way to retain their business (and it's a far smaller cost for the customer in the short term, win-win).
Some customers will buy a membership for someone else, usually parents will buy it for their kids so they can come and play without having to borrow their parent's credit card.
I could go on.
Pricing the membership is the hardest part. I'm still experimenting. Recently switched from monthly to weekly payments so we'll see how effective that is. It sounds nice having it as a lower number compared to the monthly price!