RollKur/Hyperflexion

The other day, my young dressage students who are also 4H members came and asked me about Rollkur. Well, I'd never herd of it, but after seeing some videos and pictures on youtube, I am more than a little disturbed by this training method; however, I know nothing about the logistics of it. It seems to be very wide spread and used by Anky and Isabelle at the International levels.
Can you please help me to understand the theory, practicality, benefits and risks to using this technique?

I recently added this discussion to the main page. Barnmice Admin recommended that I add it to the dressage groups and broaden the discussion. I am only glad to do so and look forward to the feedback!