[lmilcin]

It's only "wasted" if you can show that they would have done more if they didn't spent those 10% on breaks.

The reality is that most people don't do more by skipping their breaks. They just start working more slowly or their minds drift away. This is more true for people doing creative jobs which is more and more people every year.

I'm software developer solving relatively difficult problems, I can really focus maybe 2-3 hours every day on real work. I spend the rest trying to do mundane stuff, learn things, talk to people, etc.