Angular 4 component reference into another component

I have a question about Angular 4 in general.

One of my co-workers created a reference of an AComponent and bound it as a property to a BComponent to access AComponent's properties, instead of binding AComponent's properties individually. Then he also subscribes to an observable in the AComponent.

Here is the idea:

// a.component.ts
@Component({
  selector: 'some-a',
  template: `<some-b [someRefToAComponent]="someRefToThis">...</some-b>`
})
export class AComponent {
  someRefToThis = this;
  someObservable: Observable<any>;
}

// b.component.ts
@Component({
  selector: 'some-b',
  template: `...`
})
export class BComponent {
  @Input() someRefToAComponent: AComponent;
  someSubscription: Subscription<any>;

  ngOnInit() {
    this.someRefToAComponent.someObservable.subscribe(...);
  }

  ngOnDestroy() {
    this.someSubscription.unsubscribe();
  }
}

Here is my question: Is this a bad practice or a very bad practice? And additionally: What could happen in such a case? Could it lead to a memory leak?

Would be interesting to know what happens since I don't have that deep insights into Angular's internal functionality, yet.