When I need to match seams or fabrics such when I'm connecting backing fabrics I press the seam down as she showed us and then put the other fabric face up on the table and match the folded edge to it. Once I have it the way I want it I add a spot of Elmer's glue along the edge and press. This way I don't have to use straight pins and hopefully the fabric will not move as I stitch it down. Most times it works like a charm for me.
Great video though.