What is NgZone in Angular? When and why would you use ngZone.runOutsideAngular()?

NgZone helps Angular know when to trigger change detection by “zones” wrapping async operations
For expensive operations (e.g. scroll, mousemove, animations), you may run code outside Angular so change detection doesn’t run on every event
Then when you need to update UI, call ngZone.run()
Be careful: code outside Angular can’t call Angular APIs that rely on zone unless you wrap them