Mental garbage collection is the cleanup the brain runs while you sleep. This is not a metaphor I am stretching: during sleep the brain physically clears metabolic waste built up over the day (the glymphatic system), and memory gets sorted and consolidated. It is the offline pass that keeps the system from filling with leaks.
Skip it and you do not just feel tired. Working memory shrinks, judgment narrows, and the next day your thinkput drops, measurably, whether or not you feel it.
Which makes the grind-harder-to-keep-up-with-AI plan quietly self-defeating. Sleep is not the hours you are failing to work. It is when the brain does the maintenance that makes the work worth anything.