Keeps my seams from coming apart. I swear by them. I’ve had quilt tops that I’ve drug around to several stores looking for border fabric, backing, etc, and no matter how much I abuse them on those trips with opening and refolding I’ve never had seams come apart. I only use a 2x4 inch piece of fabric that I fold in half to make a 2x2. Criminy, I’ve thrown scraps away bigger than that. Why not put them to good use!