Certain cultures, particularly those in hot climates, have systematic nap times, or siesta. A 15- or 20-minute sleep in the day can for some improve alertness, sharpen memory and reduce the symptoms of fatigue. Some people may need more or less time. Humans are more likely to nap after lunch.
Midday napping is a cultural practice in China and it is built into the after-lunch schedule in work and at schools.
Multiple short naps (between twenty and thirty minutes every four hours or so) can reduce total sleep to two or three hours in the 24 for weeks on end without detriment to a person's overall performance.
If getting to sleep or staying asleep at night is a problem, naps are probably not for you.