KENNETH CHANG discusses this in an article titled in today's NY Times.
Leap seconds are needed because Earth's rotation is slowing down and the second has been defined most recently by natural vibration of Cesium-133. It was was first defined as a fraction of a solar day, hence, no need for a leap second.
Chang's article describes the conflict going on between warring parties, mainly Briton and the U.S., with regard for doing away with the leap second. There was supposed to be one this year but the governing gurus decided to put this off until 2015 in the hopes that they may come to some agreement.
Before railroad schedules in the late 1800s, time was set in each town by when the sun was directly overhead. There was no worldwide synchronized time. I sometimes wish we would switch back to the old method. But that would be saying time is irrelevant!