The LED headlights draw less current. On cars with fog lights, they are supposed to turn the fog lights off when you turn on your high beams. However, there is not enough of a load to trip the switch so you can change between the high beam and the low beam when the fog lights are on so you just end up with high beams and fog lights on. Adding one of these will allow you to have the fog lights on and change between the high beam with no fog lights and the low beams with the fog lights.
Only one needed per car.