I took this from Amars update.
QTS is VERY SERIOUS thing, it's not just a "quick setup". It allows you to adjust almost everything we know from "big" games to almost any car in almost any race.
You can adjust Power, Weight, Tires, Aerodynamics (on tuned cars only and F2007 I guess), Ride Height, Spring Rate, Damper, Toe, Camber Angle, Brake Balance, F/R Torque Distribution (I presume for 4WD cars), TCS, ABS and Transmission (all gears + Final Gear Ratio). Also, you can adjust Max Turning Angle for wheel, which is aimed at drifters at the first place. In short, QTS allows you to think and mess about your car as fully-modified-car from "big" GT games. It also sets the ground for all newcomers, who will thisway get the basics for car-setting once when full-game is out.
Hope it helps