Using ng-click vs bind within link function of Angular Directive

You may use a controller in directive:

angular.module('app', [])
  .directive('appClick', function(){
     return {
       restrict: 'A',
       scope: true,
       template: '<button ng-click="click()">Click me</button> Clicked {{clicked}} times',
       controller: function($scope, $element){
         $scope.clicked = 0;
         $scope.click = function(){
           $scope.clicked++
         }
       }
     }
   });

Demo on plunkr

More about directives in Angular guide. And very helpfull for me was videos from official Angular blog post About those directives.

I think it is fine because I've seen many people doing this way.

If you are just defining the event handler within the directive, you do not have to define it on the scope, though. Following would be fine.

myApp.directive('clickme', function() {
  return function(scope, element, attrs) {
    var clickingCallback = function() {
      alert('clicked!')
    };
    element.bind('click', clickingCallback);
  }
});

Shouldn't it simply be:

<button ng-click="clickingCallback()">Click me<button>

Why do you want to write a new directive just to map your click event to a callback on your scope ? ng-click already does that for you.