To give our bodies the rest it needs in order to function properly at it's full potential
Because when the day finish we need rest for our body. We are awake for 24 hours which is a long time and we get tired and we need sleep.
Sleep is a natural state of body consciousness, many people debate it's purpose but it is quite clear if you look at this.
Body: When you sleep your body runs a check, twitching, rolling, muttering. This is your body determining what to fix and checking if everything if repairable or intact. Afterwards it repairs the body as best as it can during sleep. When our body is rested, just like with disease, we heal better when resting.
Mind: Sleep for your mind means that the brain check the hormones and brain function from the day. Your brain also sorts information from the day, and checks you system reactions and reflexes, which is why when you don't get enough sleep you forget things and have a slower reaction time.
In the day you waste lots of energy.
And you need time to recover.
You sleep for several reasons. Of course , to rest from the days activities. You also grow in your sleep and repair damage or stress to the body.Dreaming also allows you to deal with unaddressed problems or emotional issues. We all need good, sound sleep. Sleep deprivation is used as a form of torture, and in extreme cases will induce psychosis. So get adequate sleep. It is important for your physical and mental health.