Most conversations about working fewer hours are really conversations about how much the personal resources of workers can be drawn upon without providing extra pay before there are negative productivity consequences. This article ties in directly with some ideas I've been exploring recently [0] involving personal resources of workers and time/productivity management of workers [1][2]. The concepts of worker personal resource management and worker time management are largely foreign to the places I've worked, much to their detriment. Instead, the strategy could be described as "colloquial management", a mishmash of half-remembered concepts from business school or worse, the playground.
If a worker can quantify roughly how much time and energy each task at work will take up, a clearer picture of how to be the most productive in the least amount of time will reveal itself. Employers perpetually hide in the ambiguity of the employees' time and effort, hoping to make a profit out of asking for too much and motivate their workforce by periodically throwing a tiny bone to the most masochistic over-achiever. A tabulated rubric describing to the employer exactly how much time is spent on each task and how much mental and physical energy the task takes relative to the worker's actual capacity for these energies would show exactly how wasteful it is to over-work people.
Longer hours deplete worker mental energy and physical energy resources whether or not there is more work being done. Once these resources are depleted, worker efficiency drops precipitously. Additionally, periodically depleting these resources leads to worker burnout. I also suspect that workers resent longer hours whether or not they are necessary, leading to weakened ability to refill their mental energy reservoir due to poorer mental health in general.
[0]:http://cryoshon.co/2016/01/04/how-to-survive-late-capitalism...
[1]:http://cryoshon.co/2015/12/23/time-management-tips-hot-from-...
[2]:http://cryoshon.co/2016/01/01/how-to-decide-what-to-prioriti...