When miters are glued up they tend to open at the tips because end grain has been cut on the diagonal. These little spring miter clamps are perfect for keeping the pressure on while gluing miters, and when the glue is dry the tips will still be together. The sharp points pierce the wood without cutting wood fibers so it's easy to clean up the marks.
The handy Miter Clamp Pliers. It takes a pretty strong thumb to open our miter clamps wide, (they will open nearly two inches by the way). Many users, including lots of big strong guys, like the ease of operation that the pliers allows.