She uses it to help her get the perfect 1/4 inch seam allowance. Please don't just take this idea and use it though without clicking over there to see her tutorial on setting up your machine. She has some very good pictures and hints at setting it up accurately. Plus, you are going to want to get this stuff off some day, and she tells you how.
Click HERE to see the whole post. Thanks Karen.
Also, I took a class from Susan Cleveland, not only an expert quilter and famous for her piping hot binding and curves, but she is an engineer. She has the skills and mind to figure out amazing things. As long as we are on the suject of 1/4" seem allowances I want to share one of her tips. Do you use a 1/4 inch foot on your machine to piece that has a bar to stop the fabric at 1/4 inch? I do. I have been using it for a long time, but not any more.
She pointed out that when using that foot your fabric is not being grabbed by all of the feed dogs. This makes for less than perfect feed. Instead, she put another wider foot on, moved the fabric to the edge of that foot (to the right of it) and found where the 1/4 inch mark is when the fabric travels all of the feed dogs by simply adjusting your needle then to that point and put Post-It notes or something like the insulation trim pictured above to stop your fabric right where the right edge of the foot is. What a difference this made! This turns a regular foot into a quarter inch foot with perfect feed, because you get to use all of the feed dogs. I hope this makes sense. If you are having trouble understanding this, please let me know, and I will post some pictures.