I find it very practical as far as ground work. Just a wiggle of the rope, and the horse backs up. Simple and easy. And you won't always have to wiggle the rope, with my horse all I have to do is square up to him and give him a look and he backs up. At one time I did have to wiggle the rope, but I always started with the look so that eventually all it takes is the look.
As far as it translating into the saddle, sure, wiggling a rope doesn't do it, however in the Parelli system they have seperate exercises for in the saddle that teach a proper back up.