Sleep also somehow helps the immune system do its thing properly. After a night without sleep or a few days with insufficient sleep, the immune system is partly compromised. As one example, multiple people I know with chronic virus-caused skin conditions (like warts, herpes, ...) have symptoms when they don’t get sufficient sleep. I know a couple people whose arthritis kicks into high gear after insufficient sleep.

Sleep also definitely has a large effect on mood, I assume at least partly through the mix of stress hormones produced; many people I have known closely become extremely emotional and irritable when they haven’t had enough sleep. Others become emotionally detached/withdrawn (at least, by outward appearances).