The log might mention how I came to the book, what the big themes were, and for non-fiction, I write down the page number of important points that I might care to reference later.
This might be really weird but when I have a tough question, I like to think about what my favorite authors in my library might say, and I'll take the book out and flip through the pages, looking for their thoughts on the subject. When I spend hours reading a book, I internalize that author's voice, beliefs, and thought process. I don't need to remember all the tiny details but I remember their thought process which I consider priceless. I was going through a book called Seeking Wisdom: From Darwin to Munger and they have pages of questions to ask in the back and I realized I was automatically asking all of them on a daily basis. I had internalized that thinking.
Just because the density is better doesn't mean every book is dense.
In terms of memory, I keep notes and titles in Goodreads. Over time I may use a more durable store but I enjoy Goodreads.
I don't know if I agree. It just seemed relevant.
Do you not get tired from this?
Books I read 3 years ago are typically purged from memory by now. What remains are understandings and intuitions on a topic, which have value, but sometimes I wonder if the time is always well spent.