After reading two unrelated posts on ArsTechnica, my brain thinks they could be similar leading to another post trying to relate them.
Recalling memories while asleep helps lock them in place: "Memories can also get replayed while we sleep, which is thought to influence their long-term storage. A study released over the weekend suggests that recall during sleep has a completely different effect from conscious recall."
So human brain recollects all crappy things we had experienced all day, tries to delete unwanted ones and archives the ones which are relevant. This explains why I remember the girl in another floor but not my manager. And why staying awake long tires the brain, archiving running parallelly?
Ask Ars: Of solid state drives and garbage collection: "most SSDs engage in 'idle' or 'background' garbage collection"
SSD's seems to be doing similar stuff as brain. Keep writing data as long space is available and delete them later when idle. All is done to improve SSD life.
Both brain & SSD seems to be doing idle garbage collection without the user knowing about it.