The Most Underrated Guitar Effect

If you had to construct the ultimate pedalboard, what types of effects would you target? First instincts may lead us to distortion, delay, phase, wah, or flange, while others may be more clever with their answer, remembering a tuner, volume pedal or even a noise gate. There's one effect, however, that often goes overlooked on a pedalboard, and it's one that I absolutely can't do without. What could it be... ? Hint: Empress Effects makes a damn good pedal with this effect.