I created sad-hover component which is really sad at the moment. Here is stackblitz https://stackblitz.com/edit/angular-sad-hover?file=app%2Fapp.component.ts Open developer tools to see console output.

Problem:

1. I have isolated sad-hover component which uses OnPush.
2. Inside it I use (mouseleave) and (mouseover) and I don't want to trigger my whole app change detection to run.
3. This component is used in parent sad-cat component, and sad-cat is used on root app component.
4. It turns out that zone is still grabbing these events and triggers parent component and root to update.

Solution:
Allow to have truly isolate component so everything that I make inside will stay inside, but I'm still be able to notify parent components about changes by using @Output();
One solution could be to allow inject zone and say than I don't want to trigger any parent's component's CD.

class MyIsolatedCmp {
   constructor(zone: NgZone) {
      zone.SkipParent();
   }
}