Sleep is not wasted time. During sleep, the brain helps consolidate memories, regulate emotions, and restore critical biological functions. The body also performs repair and maintenance processes that are harder to sustain during waking life.

Researchers still debate every detail of sleep's purpose, but one thing is clear: chronic sleep loss harms attention, judgment, mood, and health. The fact that evolution preserved sleep across so many species suggests it is not optional luxury—it is biological necessity.

Reference:

Wikipedia: Sleep

https://en.wikipedia.org/wiki/Sleep