Yes, you could order a drink at Leaky Cauldron and then sit as long as you want, but their procedure does eliminate the entire someone-sits-at-a-table-and-saves-it-while-someone-else-gets-the-food scenario. I'm willing to bet by eliminating that time on the front end, Leaky Cauldron is able to turn tables over faster and it completely eliminates the possibility of people sitting in the area and using it as a "cooling off" area as another PP suggested in prior threads.
Interesting that Satul'i stopped patrolling the inside of the restaurant. Yes, we were there in August 2017 and there was a CM with a stanchion and rope who was only allowing people with Satul'i food into the seating area.