Because it's just as vital to our existence and well-being as food, air, and water. Our bodies and brains need to regenerate.

Recent studies show that the brain prunes connections between neurons while you're asleep. That's the core purpose for it.

When awake, when doing things you need adrenaline, the complex interaction of neurotransmitters is a bit beyond me, but basically, some prevent us from putting energy into restoration, so they have a day and night shift. Daytime guys keep us alert and active, when they clock off, when we sleep, the night shift comes in and fixes all the damage the day shift caused.

I have read this and entertained it, During the day our body requires a lot of energy awake and that allows enough oxygen for the brain to function clearly, Though when the brain is not getting enough oxygen it puts the body to sleep , eliminating that extreme energy draw. Now the brain sends out hormones that evening and the next day we are ready to go.

I subscribe to the school of thought that says during sleep your brain organizes the day's gathered information. That is probably a very over simplistic way of sayign it, because the process itself is much more complicated. That may not be the sole purpose of sleep, there may be multiple purposes of why we need sl;eep.

I think its to help your brain reboot because you can rest your muscles without sleeping

Scientists have been studying this for years and don't know why. My theory is that it is a daily stress reliever. The more we get, the better we feel.

[iflscience.com]

So, we don't crash our cars and die.

Body can do maintenance whilst we sleep , brain needs to sort it's files out. Plus it's feckinn awesome . That's my scientific opinion ????

It gives our bodies and minds time to recover from the stresses of life.

During sleep is when the body does a lot of self-repair. Of course we need sleep.