my brother was, long ago, in the military flying 'copters

they had very strict rules about the amount of time you could fly in a combat zone vs the amount of time rest you needed to take. the point was that the risk of someone tired making a bad mistake and costing the lives of other people, as well as losing expensive equipment, had been measured and limits set.

of course, people working in IT are unlikely to make mistakes that cost lives, but they can be very costly to businesses. at one bank datacentre I used to visit, an electrician got electrocuted and the emergency power was hit, and the bank took many hours to bring everything back online, costing them (estimated) 10's of millions of $$$. At that data centre we had a server whose motherboard fried, emitted lots of smoke, but we managed to prevent the fire alarm going off and causing the power to shut down automatically - phew!