Would you rather two pilots who on final approach can't keep their eyes open because they are so exhausted.
When you are driving a car and get the 'nodding dog' effect and scare yourself sh*tless when you fall asleep for a second or two do you pull over and have a few minutes sleep or do you push on regardless.
It is actually the safe thing to do when you are over the middle of the ocean in the pitch dark with no-one to talk to except for a radio call every hour or so to use the time to have a few micro naps so that when you are expected to land the aircraft with 300 people down the back at 05:30 you at least are awake to do it.