Yes Nick, it adjusts for speaker levels and distances and goes a considerable way toward equalizing room and speaker response variations from flat. A sound level meter wouldn't be needed for the set-up, since it's automatic, but it's good to have one anyway to see what the sound level actually is.
No, any "tweaking" is likely to make things worse. This is despite the fact that on some other boards I've seen comments about how when they checked the auto-calibration by doing it manually with the meter, the auto was only "off" by a dB or so, based on the highly dubious assumption that their manual calibration was the more accurate one.
