I reread for various reasons. One is to sort revisit an old friend. Just as I enjoy watching reruns of M*A*S*H or whatever, I can enjoy a story all over again, but a great book is particularly enjoyable to reread. Also, when I reread a book I know that it's going to be a good book! It is also nice to be in the company of the many characters found in great books, such as Atticus Finch, or Huckleberry Finn, or Yossarian from "Catch 22".
Some of the books I have reread are "Pride and Prejudice," which I think I have read about 4 times (I lost count); "The Moviegoer" by Walker Percy (which I actually liked less the 3rd time around); "Day of the Jackal" by Frederick Forsyth; "The Giver" by Lois Lowry; "Moby Dick" (a really great book--I don't know why it has this awful reputation, except that we are forced to read it in 10th grade when we'd all rather be doing something else); "The Name of the Rose," (what a wonderful book--talk about always finding more to dig out!); and "To Kill a Mockingbird."
