AngularJS使用$rootScope作为数据存储

Occasionally there are pieces of data that you want to make global to
the whole app. For these,you can inject $rootScope and set values on
it like any other scope. Since the scopes inherit from the root scope,
these values will be available to the expressions attached to
directives like ng-show just like values on your local $scope.

看来，团队鼓励使用$ rootScope这种方式，与这个警告：

Of course,global state sucks and you should use $rootScope sparingly,
like you would (hopefully) use with global variables in any language.
In particular,don’t use it for code,only data. If you’re tempted to
put a function on $rootScope,it’s almost always better to put it in a
service that can be injected where it’s needed,and more easily
tested.

Conversely,don’t create a service whose only purpose in life is to
store and return bits of data.

这不会对$ digest循环(它实现基本的脏检查来测试数据突变)加载太多，这不是一个奇怪的方式来做事情。

编辑：有关性能的更多详细信息，请参阅此答案从Misko(AngularJS dev)这里在SO：AngularJS : How does databinding work?具体注意性能部分。