The location of the Buick brake rotors and discs is on the inside of the wheels on the four corners of your suspension system. This is the part of your braking system that the friction is being applied to and the kinetic energy moving your vehicle forward is slowed down. To minimize the wear of the brake pads that apply the pressure, the brake rotors should have a smooth, flat surface. This is how they come from the factory. If your technician informs you the rotors or discs on your Buick need to be turned then groves must be present on them. This can only occur if the brake pads are worn out and the backing plate of the pads has made contact with the surface of the brake rotors and discs for a period of time. As a driver of your Buick, you should have heard a grinding noise coming from the brakes and the reason for the visit to the mechanic's shop. If this did not occur then inquire why the brake rotors and discs need to be turned. This is a procedure that should only occur when necessary and not part of a routine brake job. Each time your Buick brake rotors and discs are turned, the thickness of them become thinner. There is a minimum thickness for this auto part to be so sufficient cooling can occur. Once the disc brakes become too thin, they have to be replaced to ensure the braking process occurs correctly. The thickness of the rotors is listed in the manual for your Buick. Ask what it is, and make sure your technician measures your brake parts accurately so the right decision if turning or replacing should occur.