Those daily long lunches were time/place where on rare occasion ad-hoc discussions would lead to a new way of doing something, a new (micro)service ...
Basically the type of synergy/innovation that is typically thought by business that it happens by the water-cooler.
On the other hand, in my experience and observations - just one or two of 2-3 days hackathons (so total of <=6 work days) produced almost an order of magnitude more synergy/innovation than those daily (long) lunches during the rest ~5 years of workdays.
Though sure - some things like initial employee onboarding (or even internal move to different unit/team), trainings/workshops, (semi)annual or quarterly plannings...etc are usually better in person.
Yet I've basically never had any of those at office desk. It was either bigger conference room (or dedicated auditorium/presentation/workshop room), or a meeting/lunch with manager or a (more) senior person with one or two of "newbies".
After initial onboarding (which is usually a week or two of "newbie" not being at desk with the rest of their new team).
All of those things add up to 1-2 days in office per month (including giving talks/training/workshop to "newbies").
Add 1 day for interviewing candidates F2F, and we're up to 2-3 days per month.
Even if you have a hackathon each month ... And the most I've seen was 2-3 days once a quarter, though usually it was 2-3 days per half a year - so nothing close to mythical Google 20% of the time ... We're still talking about at most 4-5 days in office per month.