New Variable Input Impedance gives guitarists eight selectable options to enhance their tone. When set to "auto," the impedance matches that of the first amp or effect in the chain, creating the same response as plugging into the modeled original. Seven discrete resistor values (22k, 32k, 70k, 90k, 230k, 1M, 3.5M) can also be selected to further sculpt the sound, actually changing the analog circuitry. Impedance settings are saved with each preset.
These settings are very valuable in tweaking your tone, with my Strat, I lower the value to around 32K on some patches and achieve the tone that I was set out to create. If you find that a particular patch that you are working on is a little too bright or thin and adjusting the amp or other Eq settings is not working for you, experiment with these settings and I think that you will be happy with what you find.
They react quite differently depending on the pickups that you are using and the amp and effects models that are in your patch.