In startup environments crunch time has a nasty tendency of becoming normal time, and you get nosediving morale, massively increased attrition, and lower overall productivity. It's lose-lose all around.
So sure, in a startup you'd expect some late nights. When late nights become the norm though, you are now officially in dysfunctional company territory - don't let naive founders with rainbows and unicorns in their eyes convince you otherwise. Very sick of this Valley attitude that you must push yourself to the very edge of death-by-exhaustion to achieve anything worthwhile.