Is it necessary to implement imagePickerControllerDidCancel?

While working on a simple app where you open a Photo Library then choose an image I faced with a function imagePickerControllerDidCancel.

As I understand this function will be performed upon the click on "Cancel" button (while Camera or Photo Lib is open). And inside this func you need to perform dismissViewControllerAnimated.

func imagePickerControllerDidCancel(picker: UIImagePickerController) {
    dismissViewControllerAnimated(true, completion: nil)
}

But i tried not to implement it and the button Cancel was still working as it supposed to.

Is it necessary to use imagePickerControllerDidCancel or what is it for ?