The first Korn album is a great example of the power of imperfection and its relation to performance. You have a drummer playing with no click and a singer that does everything wrong from a technical perspective - improper breathing patterns and enunciation so jumbled it sounds like he's singing in Japanese. Add to that sloppy over-effected (and sometimes slightly out of tune) guitars and bass and you somehow have a product that is raw, out of control, emotional, and darkly beautiful.
No performance is perfect, and tiny imperfections caused from an energetic and emotional performance can add a level of impact to the music that all of the gear and editing in the world won't give you. Ross Robinson created a masterful work of art by finding and enhancing those small, interesting flaws in the performance and turning them into hooks. He amplified and enhanced things like the "whooshing" background noise from an MXR P90 through an unplayed Marshall head (listen closely to the left channel during the middle of "Blind"), ground loop hums, and the sound of cables being unplugged. And he managed to do it in a musical manner. Awesome stuff.
Performance truly is everything.
My .02$
-Lance