You want to watch a movie. It's part of a trilogy. Or a saga. You can't just watch one. You have to get them all and go through from start to end. So you call everyone round. You want drinks. Food. You want Hobbits on your pint glass? The Millennium Falcon? Ours come in packs. You get the idea. Handy if you run a themed pub, or have a geek brood to cater for.