I don't need more than one copy of a beloved book series....(But how do you ignore the new artwork on new editions?)  However I do have this habit of rereading my favourites. I found a particular series in my mid-teens, a lonely 4 year period for me in a foreign country, and  that world and its characters became MY world. And perhaps I justify spending weeks each year revisiting. My original copies fell apart and so the first replacement was necessary. As I've aged I've become a collector of Tolkien, Rowling, Jordan and Tad Williams. My personal go-to's. I feel I can't spare the emotional investment into new works by other authors, I just stay with those close to my heart or I write.