I think the afghan stitch is simply fascinating. Aesthetically, it's an attractive stitch; it has interesting horizontal and vertical elements which shine through whether you are working with a single color, or multiple colors. There are many creative ways you can use this stitch; its intriguing texture is well-suited for a wide range of crochet projects, from simple and utilitarian to fancy and intricate.
This stitch is made using a long Tunisian crochet hook; it belongs to the family of Tunisian crochet stitches. If you'd like to learn more about Tunisian crochet, my Tunisian crochet overview covers some additional information you might find interesting.