It's like the eye doctor test; 'better.... or worse' when comparing things with or without parameter changes.
I use it a lot on high gain patches (motor drive). I usually have it set from 2.5-5.0. I can't really put it into words, but it doesn't something to the tone that would be hard to replicate with just EQ. I find it nearly essential for a lot of "modern" metal types of tones.