From The Literary Hub:
I own multiple copies of books—Stoner, To Kill a Mockingbird, and The Catcher in the Rye. There are personal reasons I will cherish each of them for the rest of my life.
One friend called the books she has in multiples “a little family of weirdos who all sit on the shelves together.” Another keeps out-of-print multiples and updated copies of the same books. Many people buy multiples because they travel and want to have copies on the road; others buy multiples of books they adore because they intend to give them away, although they often end up holding on to them for reasons they don’t understand. Certain books are collectibles. Different translations of the same books, signed editions, and several artful covers are reasons to double and quadruple up.
But probably my favorite explanation for multiples comes from a man who “rescued” a hardcover of a book he already owned from a pool hall to rectify the “great injustice that such a good book was just sitting there in a billiard parlor having been bought by the yard with hundreds of other books as wall decor.”
Link to the rest at The Literary Hub