Right, I find this description as confusing as you. I think it describes the ideal world with no network delays and timeouts, no animations and layout issues.
The description originates from the following:
Protractor runs an extra command before performing any action on the
browser to ensure that the application being tested has stabilized.
This extra command is an async script which asks Angular to respond when the application is done with all timeouts and asynchronous requests, and ready for the test to resume.
Now, what does that "application is ready" statement mean? It basically means that, there are no pending requests, promises and "macro tasks" inside the Angular running application (source for angular testability).
From what I understand, this helps to cover most of the timing and waiting issues, but, if there is a pending JS code executed outside of Angular, or if there are any pending animations or other UI-related changes - this may potentially have an effect on your test stability - for instance, an element might not be yet visible or clickable, an input may not yet get enabled etc.
And, this does not actually contribute to the feedback from the end-to-end tests being stable and helpful - for example, in our project we often find ourselves adding browser.wait()s here and there to tackle occasionally failing tests. Also, here is a set of things that helped us to tackle this flakiness:
