Let One Idea Travel Across Books
You read two books that both touch on how to prepare for a meeting, and your notes go into each book's file. The next time the question comes up, you have to remember which book said what, and the two notes never meet.
Andy Matuschak's working note "Evergreen notes should be concept-oriented" argues for filing notes by concept, "rather than by author, book, event, project, topic, etc." Notes filed by book don't accumulate: a second book on the same concept gets a new note, and you end up with "a scattered set of notes on the concept, perhaps referring to it by different names." Kept apart, nothing pushes you to combine them, or to ask, as he does, "Is there tension between them?" Filed by concept, notes can also link ideas from very different books that share only one point. He is upfront about the cost: it makes note-taking "a little harder, but in a useful way," because each new note has to find where it fits into the whole.
My takeaway: ask what idea a note is about, not which book it came from. If one book says "plan every minute" and another says "leave room to improvise," one note on meeting prep can hold both, each still marked with its book, and the tension is right there to think about.