To recap:

   - 8hrs for work;
   - 8hrs for leisure (daily commute, family time, hobbies etc);
   - 8hrs for sleep.

If someone decides to misallocate rest time, then s/he will become sleep deprived leading to low productivity. This is true regardless of whether you perform physically demanding work like farming or sit all day at a desk doing knowledge work.

A self-inflicted impairment like this is no different from abusing hard drugs or consuming too much alcohol (on or off the clock), but it is vastly different from low productivity resulting from falling ill, which is beyond any employee’s control.

Whether you like it or not, paid employment demands a certain monopoly of your time. The only way to opt out is to work for yourself.