> Many office workers spent some 50-80% of their work hours on overhead (meetings, email), leaving very little time for actual focused tasks, things that actually need to get done. When you work one day less, you just optimize the overhead part whilst still outputting the same net productivity.
If it were that easy to cull out the overhead it'd be done by now in the existing 5-day week.
I can see no reason (and none is presented in any of the comments) why moving to a 4-day week will suddenly reduce pointless meetings. It's asserted as fact multiple times, but it isn't.