When the movie came out, Hitchhiker's Guide to the Galaxy had already been a radio show, a TV show, a book series and a computer game. So why make a movie? For the amazing spectacle of planet-making technology, judging from this clip.
Arthur Dent visits the "factory floor" where his new friend Slartibartfarst creates custom-made planets. You can see partially completed planets in the distance, but there's a whole planet scrolling underneath their little space trolley. Douglas Adams' imagination finally gets a worthy canvas. It's one of the few memorable moments in the movie, which managed to turn the sparkling wit of Hitchhiker's into a bland soap opera.