I can't tell you why, but when I have the TV on or a movie playing, when I toggle between Dyn Vol on and off, the sound is more pronounced (or louder) with the setting ON.
I don't find myself turning the volume knob up as much.
One thing I don't extremely care for when it is on, is the surrounds are much louder and amplified during loud scenes in a movie, like explosions, etc... I find that when watching the movie, and there are these loud explosion scenes (or similar), I feel that the surrounds are all I can hear (because they are the closest to the seating area).
I don't know the 'why's' for all this...that's just my experience.