Here you see it in action for piping a cuff or collar, I NEVER sew a French seam that I don't use one. It helps me get those 1/8" French seams. I use it to help guide gathered fabric under the presser to keep from getting those awful fold overs when stitching gathered fabric to straight fabric. You know what I mean. It is where there are folds in your gathers or worse yet, it actually peeks out from the seam on the right side. I hate that! I use it to help ease bias around a curve such as a bib or around the lower curve of this little jacket.
But I knew it was my friend today when I was sewing the first step of a French seam. Imagine my puzzlement when I have stitched the first step on the left side of the gown and am ready to stitch the first step on the right side of the gown. You know you cut both fronts the same size because you cut them at the same time, but for some reason when you go to stitch the second side seam your front is an inch longer than the back. Don't you just hate that? How did that happen? I obviously must have been pulling on something to stretch it I suppose. Or gremlins did while I was eating lunch. Whatever.
I didn't want to puuuuuulllllll and stretch the back to fit because then when you go to press it, you can always tell. It looks like a seam with a bad case of drunk driving. So I decided to try and ease the front to fit the back. (I tried really hard to do this without pictures but couldn't help myself. Excuse the yellow cast to them, it is the yukky lighting in my sewing room at night.)
Above is an example of what I mean about your two pieces not being the same length. These are literally scraps I pulled out of the trash can.
First place the longer piece on top and use the skewer to "crowd the needle" with the fabric in front of the presser foot. You just gently push as you stitch. I am not tucking or pleating the fabric, just pushing it.
This is a closer view of the same action. I do this every few stitches all the way down the seam. Just picking up my skewer and pushing the next little bit of fabric toward the presser foot.
When I got the the end of the seam this was the difference in length that was left. This is negligible as far as I am concerned. Also in such a short piece I didn't have as much territory to cover to ease the longer fabric in. On the baby gown I was working on, I had almost the entire length of 17" to ease with. Here my scraps were only about 5" long.
See that tiny pucker I have circled? Dontworryaboutit!! It will be gone momentarily.
Nice and smooth once it is pressed.
So go to the grocery store and buy yourself an expensive sewing tool. They can be found in the aisle with the foil pans and overpriced measuring spoons.