The problem is that sleep does
so much, that even trying to create a list seems impossible, but some try:
https://www.healthline.com/health/why-do-we-sleepSleep has been researched heavily (but far from conclusively), and there is an insane amount of diseases that people who don't get enough sleep are a risk group for. And some of those correlations are quite pronounced, like being ~30% more likely to get dementia if you don't get enough sleep in your 50s and 60s.
In some cases nobody can conclusively say whether there's causation, because we don't fully understand diseases like alzheimer or some of the processes happening during sleep, but in the meantime it seems prudent to sleep a healthy amount.