Maybe you have built an awesome website or web-app and another team of your company builds an associated app for smartphones with a different web-framework and wants to reuse some of your existing components.
Building/Extracting your components as web components makes them reusable in each and every other web project.
For each component we want to extract as a web component we need a separate Angular app. From that app we can import everything we want to have in our web component from our original app: Modules, services, animations, styles. …