It is always recommended, as the expander plug being pulled through the next can cause the case to lengthen.
But with the WFT/Giraud type, is it mandatory. As you are not indexing the full case length, but just the distance from the shoulder to the case mouth.
I thought you should always re-size first...But I am still learning.
It is not always recommended to keep the expander plug(ball) in your die though. Many remove it.