Thanks, Stanley, for the interest and this question that gives me a chance to elaborate. I keep a lot of notebooks because of my work as a teacher and researcher. And I mean a LOT, and in most of them I no longer remember what I've written.

The meta-notebook comes in handy when I sift through a huge volume of my old notes. I take down notes from my old notes as I reread and re-digest them, reducing them to a bullet-point summary sometimes, revising or updating them in light of what I've additionally learned since I last wrote in those old notebooks.