Using "trackBy: index" in Angular is a good practice or not?

Using "trackBy: index" in ngFor is a good practice or not?

For example :

<li *ngFor="let error of fileErrors.value; trackBy : index;">  </li>

Using every time trackBy is necessary in all *ngFor for performance improvement or we can ignore it.

If we ignore then what will be the iterator implementation will be used by default?