Only reason I used it for so far was when mixing a clean and distorted amp sound for stereo use.
Let's say you want a distorted sound but want to add some punch and clarity to arpeggiated play, but still want stereo wideness:
You put a clean amp and a distorted amp in parallel, then XVR the clean to have the lowend on the left and the highend on the right. Then put the distorted amp on the opposite directions.
That way, the amps blend together just fine, because you have distorted and clean signal on both sides, but have a much wider stereo feel as when using both amps center panned. You don't want them hardpanned to left and right without crossover, because distorted and clean sounds don't blend well when hard panned (your ears can clearly seperate them from each other, they don't "mix up").
And yes, you could do this with simple filter/mixer blocks aswell, but the XVR block saves you some dial-in-time and cpu.
EDIT:
Another use is to seperate your guitar signal before amp inputs. Lets say you want only your lowend clean and only your highend distorted: you can abuse the XVR block to save two filter blocks in parallel here. Just place the two amps in parallel after the XVR, select input left only for the first and input right for the second and then use them both center-panned. Don't know if that saves a lot of cpu, though.
