Imagine being able to plug into two amplifiers at once, both vintage classics at opposite ends of the audio spectrum. Both do amazing clean tones, one sparkly, one spanky each with incredible overdrives. One ranges from creamy to crisp, the other from a tight grinding overdrive to a wild raunchy sound. They can take you from squishy, vintage compression to a larger range of dynamics, with the flick of a switch.
Now imagine being able to play through both at once without any phase or ground loop issues and being able to blend easily with volume pedals for each amp. Then being able to flip which preamp goes to which power amp or which power amp goes to which speaker, opening up a whole world of amazing tones.