Their function effectively becomes one of emotional/vibe meetings.
You and your coworkers are 'drunk', so whatever you say has an excuse now.
Because of the stiff upper lip, so to speak, culture of the normal workdays, you can't complain about workload, or that Steve is an ass, or that the project is pointless, etc. But with a 'drunk' cover, you can, and that information can get to the bosses and they can adjust things. That's why those meeting times are needed and all the folks need to be there with that excuse literally in hand.
Or, so I've been told by older functional-alcoholic consultants back in my consulting days.
Hey, at least the beer and gin were on the company card.
Work drinks in fields like law and finance is London are _huge_. Even in tech they're a thing. Working in a pretty no-name tech company, I've did my share of out-til-2am, home by 3am, then back in work by 9am. Less so now I just exited my 20s, but the culture lives on.
So there was an effectively mandatory work hangout every Friday evening?