reading and rereading

i will in part exchange reading pages for reading the water come kayak season, but so far am off to a happily ensconced start to the 2013 book tin.  "the architecture of happiness" by alain de botton, "glaciers" by portland author alexis b. smith and "french dirt:  my garden in the south of france" by richard goodman.  i will occasionally reread a book.  mostly after 18+ years because by then i have changed and the book holds new meaning for me.  but i realized people reread for all sorts of reasons:  remembering details, interest factor or sheer joy.  so here's the reader poll:  do you reread books and if so, what is your main reason?