I copypasted a couple points of benefits of sleep / harms of lack of sleep, but not the elaborations and reasons; check the article/website out for the rest + more info!

Benefits of sleep:
- Your body is able to repair connections between nerve cells depending on the amount of deep sleep and REM sleep you get ... (check the website for a much longer explanation)
- Obviously, if you sleep more, you will feel more awake and energetic during the day, which positively affects your mood, productivity, mental capabilities, and physical state.
- Your body repairs itself during sleep ...(read more on website)
- Growth hormones are released in sleep, making sleep vital to children, but the hormones also stimulate muscle repair for everybody.
- There are more benefits to sleep that are suspected, but they are less certain. Some of these include ... (read more on website)

Harms of lack of sleep:
- Stress (physical and mental): your body functions are stimulated to a higher level, so blood pressure may increase, you may feel your heart beating faster and feel lightheaded when you stand up, etc.
- Less concentration ... (read more on website)
- Bad memory ...  
- Impaired coordination and reflexes ...
- Bad mood and irrational behavior ...
- Trouble forming sentences and processing information ...
- Low immunity ...
- Sleepiness: obviously. Nobody wants to be drowsy or nodding off when there are things to do or teachers to not anger.

Post edited at 9:44 pm on Aug. 27, 2008 by photoFreak