Basically, the longer you force people to work the most mistakes they make. The more mistakes they make - especially in tech - the more time they'll have to spend fixing those mistakes. The fact tech industries the world over haven't figured this out yet despite the mountains of evidence shows how incompetent they are.
This is true, I thought it'd be obvious. The more tired or overworked you are, the more likely you are to make mistakes - mistakes that could introduce new bugs which needs fixing.
It's the same no matter what you're doing, even playing a video game, you are more likely to make mistakes or not see something obvious when you're tired. Working slower, making easy mistakes, etc.
It's all very very obvious to anyone with even a lick of sense.