The value of having a 40 hour work week probably depends on what you do in the other hours of the day.
If you spent all the time outside of work relaxing you will get more productive than if you spend your time outside of work in highly stressful activities.
If you employ a computer programmer who spends 80 hours per week in front of a computer regardless of whether he has a 40 hour or 80 hour work week, it might make sense to ensure that all of those hours are spent of his work.
Opensource programming in his free time comes likely out of the same budget of mental resources.
The value of having a 40 hour work week probably depends on what you do in the other hours of the day.
If you spent all the time outside of work relaxing you will get more productive than if you spend your time outside of work in highly stressful activities.
If you employ a computer programmer who spends 80 hours per week in front of a computer regardless of whether he has a 40 hour or 80 hour work week, it might make sense to ensure that all of those hours are spent of his work.
Opensource programming in his free time comes likely out of the same budget of mental resources.