There are many different models that are not meant to be the same size the as finished product, so they must be built to scale. Architecture is one area where this occurs, and the scale is generally quite small. A firm that designs a skyscraper would not be able to show the client a model of their design unless they could fit it into a room, and this is the reason scale models are built. It is not easy, and the builder must ensure each part of their creation is done in on the same scale.
While architecture is an excellent example of scale model building, it is not the only industry that uses them. Manufacturers of planes use the same scaling techniques to create their models, and large boat manufacturing finds it just as useful. Their designers can get the same visual experience from a scaled down representation as those in the car industry do with their full scale models.