Ever looked into load balancing? Basically your residential electrical service has two 120 volt coming in. The meter is measuring both of them, and whichever one has a higher load it the meter doubles it.
So if you have 1200 watts on one leg and 400 watts on the other, its not going to charge you for 1.6 kilowatts/hr, its going to charge you for 2.4 kilowatts/hr. Depending on how imbalanced your load is you could possibly save a lot of money.
I run 240 v for my lights, so that load should be balanced I think. If I am wrong please explain.