Knotted buttonhole stitch is the stitch that is actually used for… buttonholes! It creates an even line of stitches, with a stronger base than blanket stitch. This keeps the stitch stable while buttons are being pulled through it. If you are making a real buttonhole, strengthen the ends of the buttonhole with three or for straight stitches back and forth. This will help keep the hole from ripping out as you push buttons through.
Of course, it can also be played with, lengthened, shortened, widened, and used for various decorative effects. But if you are covering a cut edge, it can’t be beaten!