title: When Components or Services in Angular 2 get destroyed?
body: <p>So I checked official documentation about life cycle hook ngOnDestroy() and I get the fact it gets called on Component or Service, Pipe etc destroy. I also checked this guide here which also explains how to handle such situation correctly: <a href="https://brianflove.com/2016/12/11/anguar-2-unsubscribe-observables/" rel="nofollow noreferrer">https://brianflove.com/2016/12/11/anguar-2-unsubscribe-observables/</a></p>
  
  <p>But fundamentally I don't understand when Angular (2+) actually destroys Components? what are practical events that take place that lead to Component destruction?</p>
  
  <p>Sorry I have no computer science background and probably the answer is very obvious.</p>