Okay - I'll ask - why do you want to use A1 (or A0) as a ground?
I can think of a few examples where one might want to use two output pins to drive a device. Say a two color led that activates one color or the other depending on direction of current flow, or simulate a third combined color be switching the two output pins at significant clocking speed. I've used a small 20ma single coil latching relay where I could select to set or reset the relay depending on current direction, or once set or reset I could place both outputs to the same state to allow for zero current consumption for the relay. There are other applications where it might be useful to 'power' a device via two output pins, it just has to have a maximum current draw less then the output pins are rated for.