Imagine the scene. You're sitting at the sound/lighting/whatever desk, and some random punter/actor/director/know-it-all comes up yet again and grumbles. "Can you just tweak the 800Hz a little/The monitors sound a bit strange, is the phasing OK?/insert other bizarre statement here".
You have 2 choices. You can bow to their superior knowledge and make the adjustments. But in most cases, it is equally productive to reach across and tweak the "DFA" knob a little. Not too much, of course, just a very subtle change.
You then look the other person in the eye and state "Hmmm, yes, that's better". As they wander away, feeling superior, you can inwardly gloat, knowing that the "DFA" knob has claimed another victim.
DFA: Does Absolutely Nothing (this is a family forum, after all...)
Note: The most effective and satisfying way of tweaking any parameter on a sound system, in response to a query such as the above, is to tweak the DFA knob on the lighting desk, and vice-versa.