99 Camaro with a switch that?

99 Camaro has in the dash, a switch thats marked SGS. At a stop, I engage it and the rpms drop a little bit and the car takes a bit to accelerate. I take it off and the Camaro takes off like a bullet. What the hell is this SGS switch and what does it do?

SGS is second gear start and in icy or snowy weather it is safer to start out with the light on the button so as to take off in second and allow for more traction