Helix provides the possibility to act like a pedal board would work, which means also including the different impedance settings. For people that have a pedal board know, that pedals can have different influence on the tone.
Using a modeller this is not so obvious, and I believe the default setting is set to 'Auto'. If a pedal reduces the impedance to 250k, instead of using 1M, it will sound dull and flat lacking body. Somebody not knowing this will say, the sound sucks or the 'feel' is lifeless, etc.