Not sure why it started; but congress changed DST a few years ago to supposedly help reduce electricity needs. Apparently, the extra hour of sunlight in the evening, when most people are home, reduces the need to turn on the electric lights.
I don't think the hour of electric light gets shifted to the morning. I know once I wake up, the only light that goes on is the bathroom light (which would go on regardless of time of day because there are no windows). The rest of the house is dark.
So; hope that helps. For more history I'm sure you can google it.