A good art department saves a production a lot of money and will make the film easier on the eyes, which in turn will bring in more profit. Models save the art-dept time and money, they can be used by everyone intuitively. Models are used by art directors, production designers, directors, set builders etc... You just never know what you have, until you have a physical 3d model in front of you. When you're making sets that will cost millions, it can really count. The following pictures are of art department models I've worked on. Some of them are based or partially based on drawn plans and some of them are designed and rendered from scratch.