They're great for lining up seams when quilting.
P.S. - Thanks, Doris, for turning me on to these. They rock.
A short little tutorial about these pins:
Line up your seams so that the points will be nice and sharp. Take the pin and "straddle" it over the seam....
making sure that the bottom/back seam is lined up too. Both of the seam allowances are lined up nice and evenly between the pin. These are pretty fine pins, so sew right over them.
Makes for a much nicer corner than I could do with multiple pins. Are they going to make your points and corners perfect? No, but they can help you line up your seams with a little less effort and help ensure a much crispier point!