[judahmeek]

Yes, actually. Insects have both garbage collection & memory transfer processes during sleep. They rely on the same circadian rhythm for probably the same reasons.

And the answer to "Why not always awake?" is very likely "Irreversible decision due to side effects". Core system decisions like bihemispheric vs unihemispheric sleep can likely only be changed in relatively simple lifeforms because the cost of negative side effects increases in more complex lifeforms due to all the additional systems depending on the core system "API".