If didn't had DST it would already be light at 4:30 in summer. So in fact it would be a waste of daylight if we didn't had DST.
It's for saving energie according most of the sources I've read.
I also read that Arizona and Hawaii are the only states that don't have DST because it will cost more energie due to the aircondition. More people will use it during a longer time of the day.
----Hans