angular rxjs subscription teardown

There are different patterns for tearing down subscriptions in angular components. I've been using the Subject / takeUntil pattern, in this form:

export class FooComponent implements OnDestroy {
  private destroy$ = new Subject<void>();
...
  source$.pipe(takeUntil(this.destroy$)).subscribe(...);
...
  ngOnDestroy() {
    this.destroy$.next();
  }
}

Today I've been told to add another line to the ngOnDestroy:

this.destroy$.complete();

After doing a bit of research, it does show up on some online examples and not in others, but either way I'm failing to see the point. Looking at the source code of Subject.complete it will loop through any inner observers and complete these. Assuming we don't subscribe to the destroy$ subject directly, isn't this list of inner observers always supposed to remain empty? If that's the case isn't that call to this.destroy$.complete() redundant?