AngularJS : broadcast event from directive

In my case, I just want to broadcast an event from a directive to the controller of the view, in which I use the directive. Does it still make sense to use broadcast then?

I would have the directive call a method on the controller, which is specified in the HTML where the directive is used:

For a directive that uses an isolate scope:

<div my-dir ctrl-fn="someCtrlFn(arg1)"></div>

app.directive('myDir', function() {
  return {
    scope: { ctrlFn: '&' },
    link: function(scope, element, attrs) {
       ...
       scope.ctrlFn({arg1: someValue});
    }

For a directive that does not use an isolate scope:

<div my-dir ctrl-fn="someCtrlFn(arg1)"></div>

app.directive('myDir', function($parse) {
  return {
    scope: true,  // or no new scope -- i.e., remove this line
    link: function(scope, element, attrs) {
       var invoker = $parse(attrs.ctrlFn);
       ...
       invoker(scope, {arg1: someValue} );
    }

It's usually a good idea not to use the $rootScope as it's global and you shouldn't pollute it unless you really know what you're doing. I would recommend that you read this article about communication between services, directives and controllers.