Let's ignore the people who are automatically saying that this is useless and that techs like Boost Smashing aren't practical...(such people have apparently never been killed by a surprise boost smash the ends up being a triple hit on characters like DeDeDe, Snake, and Donkey Kong)
...now I haven't even been able to try to do this yet, but from looking at the videos, let's try to imagine how this could be useful.
1) A feinted retreat : It looks like Sheik gets some good distance here, and that she retains the ability to do any move she wants out of it. If you could feint a short hopped attack, and end up sliding halfway backwards across the stage, it could probably confuse a few opponents and maybe lure then into starting an attack, at which point you can safely let loose a barrage of needles for some nice damage. Purely situational.
(Crawl Dashing looks very useful to me, at least int he way that wave dashing was very useful for avoiding attacks...so the new discovery of this and the short-hopped version seem exciting)
2) A really cracked out approach : I'm not gonna speak to how useful this could be...probably not all that useful, but the glide motion could be used as an approach in certain situations. Not a very good one, considering you have to be backwards for it to work, but hey, I'm just exploring options here. You could probably even use it as a feint in this manner...using the slide as a draw for a shield, or an attack, cancel the movement with a tilt and then follow up from there. Possible Mindgames.
3) Has anyone seen what this does on a ledge? ...like if we initiate the slide backwards off the edge of a board? Wavedash-edgehog anyone? Just a thought...
I think this has some pretty interesting situational uses in Sheik's game. Again, like Boost Smashing, it's not gonna make her top tier, but it's another trick in our ninja arsenal that we can keep up our sleeves.