Does anyone use this, and if so, how?

Press the T.Comp button and the excessive treble is reduced but i think its a matter of taste and room/soundtrack anamolies

I think I should of said when instead of how, but you answered my question, thanks.

if you're talking about the night theatre (or whatever it's called) then it reduces the lower bass frequencies, for night time movie watching, to not disturb other who may be sleeping.

No, that is different from Theater Compensation. The night modes more correctly reduce dynamic range (it compresses the audio) so the explosions, for example, are closer in volume level to the dialog so you can still hear the dialog when played at low volume level.

Yeah, night mode reduces the dynamic range. This is the difference in volume of the quietest and loudest sounds, not the frequency response. AFAIK it will reduce the range of all frequencies the same because they all should have the same range. There is off and 4 levels of compression.

I'm a little fuzzier on theater compensation, but it's meant to compensate for extra treble that may be present in some recordings meant for larger spaces (such as a theater). I think having the extra treble can also help those sounds play through an obstruction (such as a projection screen). It's probably not needed in most cases.