In ionic1, what is the difference between abstract state and ng-include?

ionic-v1
1

For example, if I want several page of states have the same tab bar, I can do this:

.state('tabs', {
  url: "/tab",
  abstract: true,
  templateUrl: "templates/tabs.html",
  controller:function(){
    console.log('tabs');
  }
})
.state('tabs.home', {
  url: "/home",
  views: {
    'home-tab': {
      templateUrl: "templates/home.html",
      controller: 'HomeTabCtrl'
    }
  }
})

but I found I can also use ng-include to import a common UI:

templates/home.html

<ng-include src='templates/tab.html'></ng-include>

My question is, in order to have common UI in different states, when should I use abstract state and when to use ng-include?