To adjust daylight hours to when most people are awake and about.
Not everyone benefits from the change. Farmers and others who rise before dawn may have to operate in the dark a while longer before daybreak.
Some benefits: more available daylight increases energy savings while decreasing the number of traffic accidents, traffic fatalities, and incidences of crime.
Congress noted other advantages while updating legislation in 1986, including “more daylight outdoor playtime for the children and youth of our Nation, greater utilization of parks and recreation areas, expanded economic opportunity through extension of daylight hours to peak shopping hours and through extension of domestic office hours to periods of greater overlap with the European Economic Community.”
source- National Geographic News