I have known several people in my life who never re-read a book. Once they have closed the cover on the last page, they are onto the next thing--book, task, whatever. I also know of people that have a favorite re-read. My friend Alex would re-read Dune every summer. It kind of defined summer to read it, I guess. My former boss Bill would re-read The Chronicles of Thomas Covenant, the Unbeliever every couple of years.
I am a person that rereads. I do so for several reasons. First of all, I reread for pure pleasure, re-experiencing the best of what I have read. Secondly, I re-read because books don't change, but I have changed since the last time I read a book. Thirdly, I re-read becuase The book was so challenging the first time that I want to get more from it on subsequent readings.
I am currently re-reading S.M. Stirling's alternate-history Island in the Sea of Time, which I first read back in the late 1990s.
Why?
I recently finished Sword of the Lady, the 6th book in his "Emberverse" series which is loosely connected to the "Island" series and I wanted to refresh my memory of the first events in the series before I arrive at the conclusion, "High King in Montival," next year.
My Sweety recently read the book at the urging of my Daughter and enjoyed it very much. (She's not much of an SF reader.)
And I have changed in the last 15 years. I have spent several years studying Japanese sword (Kenjutsu) and I am ranked Shodan-ni in Seiki-ryu Kentutsu/Jodo. So now reading the weapon-work of Captain Marion Alston is accompanied by better-informed mental images of what she is doing.