Today I had 30 minute meetings at 9:00, 10:30, 11:30, 13:30, 14:30, and 15:30. While on the surface that looks like less than half the length of the work day in total, productivity in that 30 minute window between meetings is near zero.
Aside from the visible, practical reasons of pre-meeting prep and post-meeting notes and actions there is the harder to quantify time spent switching context between different meeting subjects and the work that should probably happen around being on camera; something which in itself is pretty exhausting.
I'm not a hardcode this-meeting-could-have-been-an-email advocate. I think tat talking out issues and plans can often yield quicker results, but if I don't have a few hours uninterrupted time to make things happen I can start to fall behind.
In creative and engineering fields, as you work you're putting together a flow of interconnected steps that eventually lead to a solution. Interruptions in the form of meetings can break that flow before it's formed and you end up back at square one. In a previous office based job a few of us had an LED beacon beside our desks as a status light: literally red/amber/green to tell co-workers if an interruption was ok.