The Double Triple Crochet Stitch isn't one that I use that often. It's handy, though, for when you need to just make some seriously tall stitches like when making some mesh patterns. I also use it for when I'm making flowers sometimes and that's why I recorded this. I made a video for a crochet rose (coming soon) and thought I'd show how to do this stitch just in case you'd never worked it before.
Oh, and it's usually referred to as dtr on written crochet patterns. :)