@Amikke rare feature on some synths, where the joystick is used to control patches.

behringe pro vs has it because the model of prophet it clones has four oscillators and you fade between them using that stick.*

* they also forgot to let you control this with MIDI, apparently, which has caused a lot of people to bang their heads in the wall who wanted to use these buried in a shelf plugged in to their computers

some have the "x/y pad" as touch panels as well. nanokey studio has it, but it was sending midi notes for some reason when i tried it.