Since I was a kid I have been told that 220V is more efficient to run than 110V but in reality, it is probably a gain so little you wouldn't notice it on your electric bill. The big overhead power transmission lines that run thousands of volts and over long distances is a whole different story. If you look at a dual voltage motor the higher voltage is exactly half the amperage but it consumes the same wattage with either voltage. We pay for wattage at the meter. One advantage is that you can use a smaller wire gauge because of the smaller amperage draw. If the 220V vac also needs 110V for whatever reason (I don't think they do though) then you would need an additional wire over a 110V circuit. One disadvantage is that your breaker 220V takes up two spaces in your panel instead of one with 110V.
