Do you think that people are spending all 40 hours of their workweek working on the most important task to increase revenue? My theory, at least with software

Do you think that people are spending all 40 hours of their workweek working on the most important task to increase revenue? My theory, at least with software engineering, is that we all struggle with burnout. You can spend 40 hours "in the office" per week, but as you get burned out, the amount of value you add in those hours decreases. If you take a day where you don't open Slack or think about work, then you reset some of that burnout, and your next 32 hours will be significantly more productive than 40 would have been. (You can probably measure it sometime. Look at the 40 hours before someone goes on a two week vacation, and look at the 40 hours immediately after that vacation.) This isn't data, but my team has one person taking every Friday off. We do Thursday-Thursday oncall shifts, and outgoing oncall takes Friday off. I haven't noticed any change in productivity from myself or our team since we've implemented this policy. One person-day per week doesn't matter much; there is probably some tiny and low priority task that doesn't get done as a result. But the important stuff keeps happening, and the team is in a better mental state the rest of the time. I don't think that 32 hours of software engineering per week would look a lot different than 40 hours of software engineering per week, averaged on the scale of months or years. 40 is an arbitrary number that has nothing to do with the mechanics of thinking about software, or even the typing-in of software. It's probably worth another look. (I have no idea how it translates to other fields.)