Quoting Diki,
" Come to think of it, perhaps THAT'S the way to get parts in and out depending on volume..? Up for one set of Parts, down for another (in the middle for both!)."

You can do that on Tyros, have 1 or 2 parts set to come down in volume as another one(s) come up - all with just 1 pedal.
It's quite useful for changing say a BigBand full ensemble eg. based on Brass/Trumpet/Sax to a solo instrument by simultaneously fading out the first two while bringing the Sax up a bit. Just switching off the other 2 alone often doesn't do a good job, since it leaves the solo instrument at the ensemble level which may be lacking for a good solo. Creates quite a smooth effect transitioning back and forth at appropriate points in the song.

John