In study sessions in school I would sometimes look things up by thinking "it was on the lower left about this far into the book." I remember studies done years ago that showed reading a physical book improved memory and learning due to the geometry and positioning reinforcing the neural paths, and anecdotally that was definitely the case for me. I don't think I'm hallucinating them, this article cites several studies that support that. Anyone who suggests PDFs are just as good "because they have pages" is missing the point - they aren't physical objects, and that matters.