My current employer is very lenient, and as a result I am very happy working here and put in more than I am required to. If they were very strict, I would work _exactly_ 9 to 5 and not a second longer - if I even wanted to work there at all.
Fact is, you simply can't be 100% effective 100% of the time. So you either end up with people _pretending_ to be busy, or people who are free to openly de-stress and are way happier employees.