DNR basically "cleans" the image of film grain. This in moderation is actually a good thing, as occasionally films have aged to a point that the prints used in restoration have accumulated excessive amounts of grain. However, the problem with DVR is that nobody seems to realize where enough is enough - and natural film grain is lost, depriving the viewer of detail that belongs in the film. The best examples of overdone DVR include certain Disney animated movies, the DVD remaster of Live and Let Die (for some reason the Blu-Ray looks miles better), and Citizen Kane.