Arizona does not change to D.S.T. What is the purpose of daylight savings time today?
It seems to me the purpose is to shift an hour of daylight from the early AM (before work, when most of us are sleeping) to the evening (after work, when we're awake), thus "saving" it so it can be better spent.
Another benefit is energy savings. Instead of sleeping through that hour of daylight in the early morning, moving it to the evening means we have the lights on an hour less in our homes, at the ballparks, etc.
I enjoy DST very much, and was very glad to hear it's extended by two months in the Energy Bill. Those who prefer darkness -- e.g. criminals, vampires, and ladies of the evening -- might have a different opinion.