Models are beneficial economically. When people look at models and see how good they look in clothes, the regular people want to be as good as the models, so they buy the same clothes. Even though they may not look as good, the act of buying the clothes helps the economy.
Fashion models are not good for society at large, but of course they tap into primal urges and are good for corporations. There is something to be said about the argument that they lead to unrealistic body expectations and have led to various social problems stemming from this phenomenon. What's good economically may not be good socially.