Have you ever been just stitching away and all of a sudden notice blood on your fabric? You have to stop and look for 1. where it is coming from, stop it and 2. how much is on my project and get it off ASAP. Once you use wonder clips instead of pins, you will never have this happen again!
I have all three sizes and use them almost exclusively instead of pins. They are wonderful for clipping fabric together instead of pins. In addition to ALL the uses listed above, I also use them to attach labels to cut pieces of my projects, especially the pieces of totes, bags, etc. Front, back, zipper pocket, inside pocket etc. Use them to clip pre-cut fabric when going to a class or workshop where they want you to bring your fabric pre-cut into specific sizes.
As you can tell, I love Wonder Clips and think they are one of the best sewing inventions in years. Oh and the bleeding issue, I don't have much sensitivity in my fingertips and can get stuck with a pin and not feel it but bleed rather easily, so it was a real issue for me until Wonder Clips came along.