This is one of those problems with liquidity. You are buying a subscription plan that tells you can come at any time. The business can't plan ahead because you haven't committed to a fixed schedule. If your subscription plan was locked to specific time slots the gym could do much better capacity planning. However, such a subscription model is less liquid which means customers want to be compensated for giving up their freedom to pick an arbitrary time slot with a discount.
It's kind of weird how liquidity is such a general concept that goes way beyond money.
