Well you can just subscribe to the theater closest to you. Why would you want to go to the ones across town?
If you're visiting the cinema very regularly, this saves money.
They can do this because they own the theatre, so when a subscription is used, it only costs them the _opportunity_ cost of one seat - which is very little, unless the showing is sold out, and they still make money on snacks. As MoviePass doesn't own the theatres, they pay the _retail_ price for every ticket a subscriber uses.
2) with reserved seating, I'm much less likely to buy a ticket if the showing is almost full, so those filled seats can reduce additional ticket sales.