A lot depends on the industry in question. For some things, a 24/7 presence is really needed - network management, many manufacturing processes, power plant and grid operation, etc. Moving to shorter working hours simply requires hiring more people to keep those things up and running. Now if hourly wages remain the same then labor costs don't change much and it might even improve hourly productivity (as tired people…
My understanding is that in the medical field, handoffs are viewed as large opportunities for mistakes to happen through miscommunication, and that's at least some of the justification behind having people work 12-24+ hour shifts.