It was first proposed by Ben Franklin to the French as a joke. I t was later taken seriously by William Willet, who said that we wasted daylight hours during the summer.
One of the major reasons given for observing DST is energy conservation. Theoretically, the amount of residential electricity needed in the evening hours is dependent both on when the sun sets and when people go to bed. Because people tend to observe the same bedtime year-round, by artificially moving sunset one hour later, the amount of energy used is theoretically reduced. A 1975 United States Department of Transportation study showed that DST would theoretically reduce the country's electricity usage by 1% from March to April, if implemented during these months. These numbers have been supported in Mexico, which began implementing daylight saving time in 1996. Evaluations show national savings of 0.7% of national electric consumption (1.3 billion KWh TWh) and reduction of peak load by 500MW.
Part of the reason that it is normally observed only in the early spring, summer, and early autumn instead of the winter months is that the amount of energy saved by experiencing sunset one hour later would be negated by the increased need for artificial morning lighting due to a later sunrise. During the summer most people would wake up after the sun rises, regardless of whether daylight saving time is in effect or not, so there is no increased need for morning lighting to offset the afternoon drop in energy usage. Another reason for not observing daylight saving time in the winter is concern about children walking to school in the dark.
Another argued benefit of DST is increased opportunities for outdoor activities, including shopping in tourist areas. Most people plan outdoor activities during sunlight hours. Other benefits cited include prevention of traffic injuries (by allowing more people to return home from work or school in daylight), and crime reduction (by reducing people's risk of being targets of crimes that are more common in dark areas).
When the U.S. went on extended DST in 1974 and 1975 in response to the 1973 energy crisis, Department of Transportation studies found that observing DST in March and April saved 10,000 barrels of oil a day, and prevented about 2,000 traffic injuries and 50 fatalities saving about U.S. $28 million in traffic costs.