I think there are variations from person to person and culture to culture (such as people who live near the arctic circle) but Traditional Chinese Medicine says people are supposed to sleep at night (when sun sets) straight through until sunrise. How much sleep is needed is wildly debated however and older people are not considered abnormal to get less. Weight loss studies have shown by measuring hormones that when a person (under 65 yrs old) goes under 7 hrs of sleep they gain weight no matter how low they cut their calories. Cortisol levels were abnormal in those with even 6.5 and even some at 7 hrs of sleep. That alone tells me that the body considers sleep deprivation a hostile thing.

I tried polyphasic sleep in undergrad. It was good for cramming for exams but useless for actually living a productive life. I heard Edison did it and was very productive that way, but i don't think his health and beauty were improved by such a thing.