People once set time according to astrology and it wasn't a problem until the rail system came about. The big wigs of the rail systems needed a better way to keep time and they came up with a standard or mean time with hourly variations according to set times in different time zones.
Benjamin Franklin observed daylight savings and suggested the idea in an essay but nothing came of it. William Willett would later observe people in their homes with the shades drawn while there was still daylight. He noted the wasting of energy and daylight. About 10 years later Greenwich mean time was used during the summer months to save energy.
During WWI daylight savings was applied to help the war and other countries followed suit as the war was costly. After the war they did away with it due to how unpopular it was especially during the winter months. Once again daylight savings would be recognized as WWII came about and some places changed their clocks 2 hours ahead of GMT. In the U.S. the clocks remained ahead by one hour even through the winter. After WWII the gov't left it up to the states to decide to keep daylights savings or not. This brought back the confusion the railways had worked so hard to mend so long ago but it had grown to also hinder the bus schedules and the radio industry. New schedules had to be made everytime a state used daylight savings and others didn't. In 1966 the uniform time act remedied the chaos.
Then in 1973 came the Arab oil embargo and for 2 years Americans followed daylight savings for a 10 month period and it did help to conserve energy. The farming states were badly hindered by it and when things with the Arabs started to look better the farmers started to complain and the 10 months long run of daylight savings was dropped.
The research during this time proved that daylight savings time did save energy in thousands of barrels of oil each day. Also noted, during the study, was the decline in road accidents as well as home fire mishaps. The study team concluded that thousands of lives had been saved through daylight savings as well as saving millions of dollars in energy savings, insurance savings and property damage.
In 2005 Bush changed the schedule of daylight savings by extending it to save energy as we work through more problems with the Arabs. Those opposing the changes are farmers and the airlines. Livestock have their own clocks they follow and when we mess with time and adjust our way of doing things farmers encounter problems with livestock such as breeding, feeding and grazing schedules. Those who farm crops and raise livestock are left to let one or the other go as they tend to one or the other.
In summary...
Daylight savings time stemmed from industry via the railways but was applied for the purpose of what is now known as the dept of transportation and their schedules. It has since been applied to most everyone to conserve energy and save resources.
Most of the U.S. and most of the world does apply DST for saving energy.