Originally Posted by pdriggs

Why? Because I'm the mommy! In garment sewing I was advised to set the seam if a long seam looked puckered. The setting took out the stretchiness. That could carry over to a much shorter seam, even if you do not actually see that it has stretched a bit. I actually do it both ways, expecially if it is on the bias. This may be one for Myth Busters.