The main purpose of daylight-saving time is to make better use of daylight.
We change our clocks during the summer months to move an hour of daylight from the morning to the evening. For the winter months it changes so that the afternoon advantage is offset by the need for lighting because of late sunrise.
The idea was that people would spend more time outside and less time inside with the lights on at night and, therefore, conserve electricity.
Longer daylight hours make driving safer, lowers car accident rates, and lowers the risk of pedestrians being hit by a car.