I have roughly ten years of notebooks in a box under my desk. They are all some kind of “bullet journal” method: date at the top of the page, items below, index in the back.
For me, only occasionally, but when I do it’s often a huge help - can save an immense amount of time not re-doing that work. Most of the value is in helping align my thoughts as I go though.
Yeah and sometimes I go back to them just for nostalgia. But truly the archiving doesn't matter all that much. I like the Field Notes tagline: "I'm not writing it down to remember it later, I'm writing it down to remember it now."