When is it safe to use $scope.$apply()?

Question

I guess the title is pretty much clear what I am asking. I have created this fiddle : http://jsfiddle.net/Sourabh_/HB7LU/13142/

In the fiddle I have tried to replica

Answer 1

All the above answers give some information but they did not answer few doubts I had or at the least I did not understand. So I'm giving my own.

It is very clearly stated in angular docs when to use $apply

the call backs of $http or $timeout or ng-click, ng-..... have $apply() wrapped in them. Therefore when people say you don't have to use $apply() when you do angular way of doing things, this is it. However, one of the answers mentions angular event handlers are also wrapped with $apply(). This is not true or by that the user means just ng-click kind of events (again ng-....). If the event is broadcast on rootScope (or any scope for that matter) outside of $http or $timeout or ng-click, for eg: from a custom service, then you need to use $apply() on your scope although $rootScope.$broadcast is also angular way of doing things. in most of the scenarios we will not need this because the state of the app changes when something happens. ie, clicks, selection change, etc... and these are in angular terms are already using $apply() when we use ng-click ng-change respectively. Handling server side events using signalr or socket.io and while writing custom directives where the necessity to change just the directive's scope are few examples where it is very essential to use $apply()