I've been tracking the books I read for the last few years. When I scan through the list, I am reminded of times and places, but also often of what I was going through in my life when I read certain books. Reading takes place in context.
Reading a book over a long time can detract from the experience, if you need to strain to remember the characters or the plot. But having nearly finished a book in one sitting yesterday on a delayed flight, I also wonder if you can read a book too fast, without any time for it to marinate in your subconscious.
One remedy for that is re-reading a book, which I actually did recently (Atmamun). I found this helped me cement certain ideas, and pick up on finer details that I missed the first time. It felt good, and I have found myself reaching to re-read more books since then (Art of Learning).
Not all re-reading is instantaneous. My penultimate book was of the other kind, as I picked up The inimitable Jeeves which I had first read many years ago. This felt more like rediscovery, uncovering half-forgotten memories. It was comfortable and soothing, though that might just be the author's brilliance, rather than a generality. I never regret reading a PG Wodehouse.