Owning multiple copies of the same book

I recently bought a second copy of a book I already own because it was available in a different format than the first one I had. This is not the first time I've done this. When I was younger, the books I bought were mostly paperbacks because they were smaller (and therefore easier to carry around and store) and cheaper. As I've gotten older, I've appreciated hardcovers more due to their durability and, frankly, the way they look on my bookshelves. Sometimes, I'll come across a special edition th...