Why should Ember.run.join be used sparingly? Why not use it instead of Ember.run all the time?


According to the guides one should wrap the content of callback originating from outside of Ember inside Ember.run call. I think I understand the reason behind this.

But now I saw that Ember Data for example uses Ember.run.join. join only creates a new run loop if there is no existing one. That seems very reasonable.

Still the documentation says that join should only be used sparingly. Why is that? Isn’t it save to use join instead of run all the time? If not, what are the use cases for join?