As I wrote newer chapters TLPI, I constantly reread chapters that I'd already written, red pen in hand. For years, I'd always have printed copies of a couple of chapters nearby to review, to fill spare moments while I was commuting, waiting for something, or just sitting in the Biergarten on a sunny weekend afternoon.
Each chapter got printed anything from around 6 to 12 times, and typically I'd read each printed copy twice, so that I could better detect ordering and forward-reference issues in the text. So, by the time the book was published, I'd read drafts of each chapter around 12 to 20 times. After reviewing each printed draft, I'd then integrate changes and improvements (sometimes informed by what I'd learned during the writing of later chapters) into the text.
I kept all those printed copies, in part because I wanted to get an idea of how some chapters progressed over time. All of the printed copies are sitting in the pile in the photo. Well, nearly all; after that photo was taken, I discovered another 15cm pile that was still sitting in my hometown in New Zealand.
Because those printouts were my constant companion for such a long time, and the writing of the book was so central to my life for a long time, I haven't quite been able to bring myself to let them go. So, for the last few years, the chapters have been sitting in three banana cartons. But, they have to go out sometime, and I think I'm nearly ready to let them go, though I'll probably keep drafts of a few chapters just as reminders.