Comment by hintymad

It not that simple. Most engineers still want to get a good perf rating. Amazon plans projects with the assumption that everyone works 5 days a week. Therefore, 4 days a week means you plan at most 4 days a week. If you choose to take a day off every week, then you will be at least 20% more productive than your peers to output at the same level. Unless you assume that your peers are 20% less productive than you, you will be at a disadvantage by working only 4 days a week.