(You think you love your sleep? If you're not Japanese - think again. The Japanese are HARDCORE SLEEPERS. Google images of "Japanese subway sleeping" for some pro-level public transport power-naps that most of us mere mortals can only aspire to.)
I've been staying up til all hours recently for a number of reasons (Diablo, nail painting, thesis - in that order >.<) and trying to make up the loss with copious amounts of coffee. While instinctively I know this is a VERY BAD THING, sometimes I need a reminder that "beauty sleep" isn't just one of those things my mum tells me...
Benefits of sleep
Learning - Are you finding it harder to remember new things you've learnt? Sleep deprivation could be the culprit. More studies are showing the importance of sleep in memory consolidation (i.e. putting things from your short term into your long term memory). One theory for this is that your hippocampus (part of the middle bit of your brain) stores new information while you're awake. When you go to sleep, your hippocampus and your neocortex (grey stuff on the outside of the brain) "talk" to each other, and the information transfers to the neocortex, which is later accessible. Kind of like typing lots of things into a new document - sleep is the "save" button which transfers all the data onto a permanent place in your hard drive.
Problem solving - Got a problem you can't seem to work out? Again, sleep can help your brain put the pieces together (technical term: "insight formation").
Butterfingers - This is an obvious one - sleep deprivation destroys your motor skills. I'm sure you've noticed it ;)
Hawtness - "You look tired" - yes, it's been proven that other people can tell the difference when you've had enough sleep! People picked pictures of sleep deprived people as being less attractive, less healthy, and more tired compared to pictures taken when they've had enough sleep. So "beauty sleep" is a real thing!
Obesity - Lack of sleep is linked to gaining weight. Studies have shown that people who regularly sleep less than 6 hours a night are far more likely to have higher-than-average BMIs, and those who sleep more than 8 hours have the lowest BMIs. Along with not exercising and eating too much, lack of sleep is one of the major risk factors for obesity. The reason for this is that the sleep-wake cycle affects many important hormones that are involved in appetite, metabolism and glucose regulation. For example, lack of sleep leads to increased insulin secretion. Since insulin increases fat storage, this will lead to weight gain, and increase the risk of getting diabetes. Other important hormones include leptin, which tells your brain when you're full, and ghrelin, which tells your brain you're hungry. Not having enough sleep (you guessed it) decreases leptin and increases ghrelin levels.
Heart problems - Heart disease and strokes are linked to lack of sleep. Even one night of sleep can cause higher blood pressure the following day in susceptible people. However, both sleeping too little (less than 6 hours) or too much (more than 9 hours) led to an increased risk of coronary heart disease in women.
Psychological disorders - Prolonged periods of sleep deprivation are linked to depression and anxiety. Several studies have shown that sleep deprivation leads to mood-related symptoms such as stress, anger, sadness, mental exhaustion, social withdrawal and pessimism, which goes away after returning to a normal sleep schedule.
Immune system - Sleeping can help you stave off an oncoming infection.
Life Expectancy - As you might've guessed from the many health effects listed above, sleep deprivation is correlated to lowered life expectancy. Sleeping less than 5 hours a night increases your risk of death overall by a whopping 15%!
J M Ellenbogen. Cognitive benefits of sleep and their loss due to sleep deprivation. Neurology 2005, 64, E25.
J Axelsson, T Sundelin, M Ingre, E J W Van Someren, A Olsson and M Lekander. Beauty sleep: experimental study on the perceived health and attractiveness of sleep deprived people. Brit Med J 2010, 341, c6614.
Division of Sleep Medicine at Harvard Medical School - Healthy Sleep Website