The Electro-Harmonix Dual Expression Pedal is designed to provide external control over two applicable effects at once. Say you have a flanger pedal whose speed parameter could be controlled by one expression pedal, and whose modulation rate could be controlled with another; if that were the case, you could use this Electro-Harmonix product to control both of those parameters at the same time, with some degree of independence.
The Dual Expression Pedal sports dual 1/4" TRS outputs, as well as two individual range knob that allow you to tune the width of the pedal's sweep differently for each output path; this way you can vacillate between narrower values using the entirety of the pedal's rocker and affect a more granular sweep, if you so choose. In fact, you could set the pedal so that it affects one connected parameter minutely and another on a grander scale, all with one rocker.
Two polarity reverse buttons are on hand to ensure compatibility with many different manufacturers simultaneously, while two reverse buttons let you change the direction of the sweep on each individual output path. Two TRS cables are included for use with the pedal.