There are lots of clever little finishing techniques that can make a project look so much better and this is one of them.  It can be used anywhere where you have the same stitches that have been cast off (or a cast on edge) and need to join them.  If the stitches are still on the needles then you can use Kitchener Stitch or even a three needle bind off, but for squares like the example shown, this is perfect!

I've used this technique in my Alphabet Sampler Blanket