Philip Shorer on the Atlantic's CityLab blog argues for a 4-day work week:
Beyond working more efficiently, a four-day workweek appears to improve morale and well-being. The president of the UK Faculty of Public Health told the Daily Mail that a four-day workweek could help lower blood pressure and increase mental health among employees. Jay Love of Slingshot SEO saw his employee-retention rate shoot up when he phased in three-day weekends. Following this line of thought, TreeHouse, an online education platform, implemented a four-day week to attract workers, which has contributed to the company's growth.
In this scenario, employees still work 40-hour weeks, but they do so over the course of four days rather than five. This arrangement still sounds sub-optimal, though, as working at full capacity for 10 hours is more demanding than doing so for eight. Despite that, the employees at Stephens’s company still preferred 40 hours in four days to 40 hours in five days. They might be even happier—and work even better—if they worked fewer hours in addition to fewer days.
Of course, counting travel, as a consultant I frequently do four 10-hour days followed by an 8-hour day. Cutting one of those out might be a good thing.