Because our application will have different clients consuming business logic, we are going to add a Service Layer; it will coordinate operations for different use cases. So, we are going to move most of our business logic from controllers to services. Probably, it's too early to see the benefits of this, but as we progress with this chapter, it will make more sense.
One benefit would be that you can simply expose your Service Layer as a RESTful API, or add another client that will render on the server-side templates and display all the necessary information to the user. Regardless of the application's client implementation, you can test the business logic of your application.