Boy, are we loyal to books we love. We cherish them like family members. My friend Maureen Phillips who writes delightful stories and poems about fairies calls her multiples "a little family of weirdos who all sit on the shelves together." (Madame Bovary, The Lord of the Rings trilogy, The Shipping News, A Confederacy of Dunces, the stories and poems of Edgar Allen Poe.)
Journalist Jeff Brown keeps out-of-print multiples and updated copies of the same books. One of his favorites is For Your Eyes Only by Ian Fleming: "It is five James Bond short stories, including 'The Hildebrand Rarity,' which I consider to be the best short story of any type I've ever read."
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 onto them for reasons they don't understand (Dolors Casas who lives in Spain but has become a connoisseur of English-language classics). Or they consider certain books (Harry Potter is very popular) as collectibles. Some, like me and Canadian critic Glenn Sumi, cherish their first editions, but read the books in cheaper paperback editions.
Ericka Clouther is married to a teacher who collects different translations of the same books, as does teacher and soon-to-be debut novelist Michael Barsa.
Like me, Goodreads friend Antoinette keeps multiple To Kill a Mockingbirds. One of hers is a signed edition. (I'm jealous.)
Julie waits for somebody to say "Oh, I never read that!" and promptly offers her multiple with the reply: "Well, here you go, friend. Get with the program."
Jazz and Renaissance man Paul Secor keeps rare editions and art books and says, "There have been times when I've considered picking up second or third copies of a book because of eye catching cover designs, but sanity has prevailed."
But probably my favorite explanation for multiples comes from Derrik (whose anonymity I will protect). "I think the only duplicate I have is Suskind's Perfume. I stole a hardcover copy from a pool hall that was using it as wall decor, but it's falling apart, so I have a paperback as well. I keep it for sentimental reasons. I thought it a 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."
In my fascination for the topic, I wondered what books are kept in multiples by some literary novelists. To find out, read my Lithub article Why Do Writers Keep Multiple Copies of Books Around?.