When you get comfortable reading a lot, you don't need to re-read books. Certainly, a rare few books benefit from multiple readings but not all. I retain a surprising amount of details and can describe passages from Dickens and the main argument of David Cay Johnson's "Perfectly Legal" or the amazing survival story of "Mawson's Will" or an amusing passage in Ernest Hemingway's journalism story "A Free Shave" or the images of the amputation tent in Tolstoy's "The Sebaastopol Sketches--to name a tiny few.

Once your reading is not going "put-put-put" and your unbroken attention span reaches an hour, you may feel like you need to re-read. Certainly, it's a nice experience but it's really a waste of time re-reading everything.