What exactly does bool parameter do in animateWithDuration:animations:completion:

I referred to the DOC and it said:

completion
... This block has no return value and takes a single Boolean argument that indicates whether or not the animations actually finished before the completion handler was called. ...

But I find that no matter you use the bool parameter or not, the completion: block will always execute after animations: block. Just like the two simple block-based animation code snippets shown below, both of them are doing the same.

[UIView animateWithDuration:0.3f
                  delay:0.0f
                options:UIViewAnimationCurveEaseInOut
             animations:^{
                 [myView setAlpha:0.0f];
             }
             completion:^(BOOL finished) {
                 [myView removeFromSuperview];
             }];

and

[UIView animateWithDuration:0.3f
                  delay:0.0f
                options:UIViewAnimationCurveEaseInOut
             animations:^{
                 [myView setAlpha:0.0f];
             }
             completion:^(BOOL finished) {
                 if (finished) [myView removeFromSuperview];
             }];

And I find that most people(including me) use the first one(even the apple's official doc example). So,

• what's the finished parameter used for here exactly?
• or what's the situation will be used?