Special effects essentially recreates physical things that can't exist, or can't exist conveniently, on a sound stage. Often times crews make models and big rigs -- or more appropriately, whatever the script calls for.
What does a bookkeeper or accountant do on a movie? "Essentially", says Michael Menzies -- veteran of such movies as Conan The Destroyer and Body of Evidence -- "my job is to work with the film's producer and the studio to create the budget. And then simply help them stick to it."