A1. They can get people's attention to promote promote products such ad COVETGIRL or REVLON, other tips of models wear designs made by designers who can have those designs sold to compies who carry that designer
A2. Physical models of buildings and constructions are very useful to provide an overview of the project. Some projects are so complex (e.g. a chemical refinery) that it is only on a scale model that the complex runs of piping may be optimized.
Models are also useful for such things as motor cars, houses, and new products.
There would hardly be a large dam built anywhere in the world without first being made in model form.