Okay there is a bit of controversy using this method. It is not new and is used commercially. The principal behind this is, if you crash chill you put the yeast to sleep straight away - in other words they become inactive very quickly. Chilling slowly allows yeast to become aclimatised to the lower temperatures and still remain active, albeit somewhat less than at the higher temperatures.
That's the first part. The second reasoning behind this is the yeast play a major role in cleaning up fermentation by-products after all the sugars have been exhausted. The one we all hear about all the time of course is diacetyl. There is also acetaldehyde and no doubt a bunch of others I have never heard of.
From my experience in making lagers over the last few years, slow chilling has a major impact on the 'clean' taste profile of a lager and also has an major impact on the 'smoothness', in other words clean, crisp but not bitey or acidic taste. Lager should clean, crisp but also smooth to the pallate.
I have tried almost all variations of lager fermentation, most at least twice and using this method absolutely trumps any other method from my experience. I do, and always will believe that the brewer makes the wort and the yeast make the beer and if you keep the yeast at their very optimum, they will produce the optimum beer.
Steve