Wetherspoons have managed it for about a decade and it’s great (I was a student... )
Things are already paid for so stops stupid people on both sides dicking around with cash. Also means they can pre-pour without fear of wastage (hot drinks with a lid on will stay hot for literally forever, you can’t drink them for five minutes with a lid off anyway, and with beer if the logistics are right then it won’t be sitting there too long).
Queues put people off. Minimise the queue and you increase sales without increasing cost. In all honesty though, selling a pint at £4 your margins is probably about £2, £2.50 at best. Selling to an additional 10k a week (optimistic), is making you £0.5m p/a. Like ticket prices, it isn’t a difference maker.