Research shows the main purpose of daylight time (DLS) is to make better use of our daylight, which varies around the globe. After instituting DLS during WWI, Congress repealed the law and DLS became optional, which caused some confusion state to state.
During WWII, Roosevelt instituted year-round “War Time” DLS from 1942-1945. By 1966, approximately 100 million Americans were observing DLS and a uniform act by President Johnson passed DLS as we know today. There’s also mention of energy savings, but I doubt that was impactful during WWI.
Don’t forget to “fall back” an hour on November 5!