That's what I thought too. But if so, why are we allowed to change it? With that said, changing it from the stock 1109mV down to 1050mV or up to 1200mV didn't seem to do anything, so it may just be there doing nothing. I was under the assumption that memory voltage is locked in these cards.
There's the thing. There's no memory voltage sensor for the 390x. At first I thought it would change the auxiliary voltage, but that's not it (plus, the 1109mV stock value would be insane for that, it's exactly 1V stock). Also, as said above, changing it to 1050mV or 1200mV didn't seem to do anything for stability, so I guess it's just a placeholder. My memory still can't overclock worth s**t, so there's that. I was just curious.