Sleep is required for proper function of the glymphatic system.[0] Insufficient sleep results in inadequate clearance of metabolic waste products from your brain via this pathway. Accumulation of said byproducts results neurological damage.

In other words, get good sleep or you're literally inflicting brain damage upon yourself. Impaired glymphatic function is linked to all manner of horrible neurodegenerative conditions.[1][2]

[0] https://en.wikipedia.org/wiki/Glymphatic_system#Waste_cleara...

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6261373/

[2] https://www.karger.com/Article/FullText/490349