(Will be editing in place)
Primary reason for sleep is re-establishing homeostasis in feed forward circuitry.
Association/Integration are not integral reasons for sleep, dreams are unchecked ventral stream prediction (hallucinations).
This looks like it’s phenotype dependent apparently. It’s not sleep so much as the ability to push delta waves, and most people can only push strong delta waves during sleep (shut down of feed forward systems). Individuals who can push delta waves while awake can associate/integrate without sleep.