Why do we use (0,+V) in digital electronics (eg processors) instead of (-V/2,+V/2)?
I think I know what you're getting at, that dynamic power consumption \$ P = C \cdot V^2 \cdot f \$ , so if you had two supplies the power consumption could be halved for the same swing at the stray capacitance. 

The downside is that you'd need more switching devices (to pull the stray capacitance to ground rather than the opposite supply), so the overall complexity would be greatly increased. If you pull it to the opposite supply, there is no improvement in dynamic power consumption. Reducing the supply voltage by 30% achieves the same end without the complexity. 

Maybe some day when they run out of ability to reduce supply voltage (it's already less than 1V for some circuits) without unduly increasing static power consumption (due to leakage), something like that might be practical. 

It's not done for exactly that reason (normally terminated transmission lines are used) but LVDS uses relatively small voltage swings (less than a volt) across a differential pair, which has a number of advantages when driving a long cable, including reduced power consumption and low EMI. Each driver swings 350mV in the below example, but the differential voltage at the termination resistor is +/-700mV.