One reason it’s good to be a master of velocity mapping (with whatever instruments you use, not just Operator) is because randomizing the velocity of an incoming MIDI signal is so darn easy. Once you’ve created a patch that responds in weird and wonderful ways to velocity messages, try dropping the Velocity device in front of it.
Now, crank up the Random knob.
Yeah, it’s that easy. You’ve now got a constantly changing part thanks to velocity randomization.