Worth Reading: https://docs.angularjs.org/guide/directive
Especially this at the very bottom of that page:
![Screengrab of Angular's explanation of link vs controller in a directive](/wp-content/uploads/2022/01/AngularJS-linkVsController.jpg)
By ‘expose an API’, they mean ‘add some this.doSomething() {…} functions to the controller that are reachable from outside the controller’. Like public class methods. If you’re not needing any of those, don’t add a controller to the directive.