The evidence is piling up that sleep deprivation impairs function. Today there is a major article on that in THE WALL STREET JOURNAL by David K. Randall. Those connecting the dots, for example, link fatal plane crashes to the pilots' lack of sleep.
We all know that all-nighters are fairly routine for associates at law firms. It can be argued that they aren't mandated. However, a smart lawyer doing discovery could collect sufficient testimony that working all night on a project could be undertaken as compliance with what is expected by the superiors and by the culture.
So, suppose you put in an all-nighter or maybe serial ones. You get into an auto accident going home from the office. There are fatalities. Your insurance probably won't pay for all of it. In fact, maybe they have read up on the research about sleep and investigate how well rested you were before you got into the car. It might sue your employer for allowing you to get into a car instead of providing a car to take you home. You might also sue your employer for that. In additional to the claims of the other parties, you might also claim your own emotional damage from the trauma.
Regulations are reducing the number of hours truck drivers can work each week. Maybe the hours should also be reduced for lawyers.