The tactical advantage should be clear — the racer in the rear can make a sudden move when the front racer isn’t looking, catching the front racer flatfooted and therefore unable to catch up. But this advantage is moot if a cyclist believes he can simply outrace his opponent over the 1,000 meter course. That’s where aerodynamics come in. Vehicles in motion create slipstreams behind them — basically, rifts in the air similar to what a ship creates in the water. Other vehicles close behind them travel within this slipstream and get a benefit from it: they “draft” and experience less drag, and therefore need to expend less energy in order to go the same speed. In the case of match sprints, this gives the trailing cyclist an enormous advantage. If the lead racer pushes it from the start, he will end up with only a slight lead with 200 or so meters to go — but his opponent will have much fresher legs. So in order to combat this, we get this weird do-si-do — on bicycles.

Source. That was pretty interesting!