At first glance the split stitch seems like a very basic stitch without a whole lot going on.  It almost looks like a smaller version of a chain stitch since it's a series of stitches that are split in half by the next stitch.  The split stitch is used in embroidery and embellishment to either do an outline or filler stitch.  It works well as an outline stitch because it can handle straight lines as well as curved lines.  It can also be used as a filler stitch as an alternative to the satin stitch.  The thing that makes the split stitch unique from the satin stitch is that it gives your hand embroidery texture.  For me, the split stitch feels the most like painting with your sewing, because, the texture it leaves, looks the most like little brush strokes.  It has a very organic flow to it and it makes it really easy to experiment with in terms of changing thread colors to get some creative effects.  Watch this tutorial to learn how to create this hand stitch.