I think it totally depends on the kind of work you're doing. If you're doing a creative, intellectually demanding job, then working for too long will burn you

I think it totally depends on the kind of work you're doing. If you're doing a creative, intellectually demanding job, then working for too long will burn you out to the extent that the each extra hour you spend working has a negative impact on your total productivity. More routine mechanical tasks don't degrade in the same way.