I have to admit (never having seen a PP video) I had NO idea where you would use/need an add-a-quarter ruler. I read "snuggle it up against the paper" and I was thinking that you were working with paper patterns that did not have the 1/4" seam allowance printed on the outside edge. So I went to the video and saw where she is using the add-a-quarter ruler.
I had never considered trimming the seam allowance on the first piece until AFTER I've attached the second piece. IOW ... I sew the seam first then just use scissors to whack off my seam allowance!!
So from my point of view I think it's an extra an unnecessary step.