It is important to break-in (or bed-in) rotors and pads properly. Not doing so can cause long term damage to the rotors and cause poor braking performance. In general, brake pads and rotors should bond with each other to provide proper braking performance. The purpose of the break-in procedure is to condition the pad/rotor outer contact surface area. On most pads used, more or less pad material is transferred onto the disc surface area as a thin padded film. Some pad compounds need to be heated to work properly as well. If the proper break-in procedure is not done, uneven pad material deposits can cause excessive noise and vibrations under braking. Uneven wear can also happen too, which can have an effect on the life span of the rotor and pad.
It is highly recommended to follow the proper break-in instructions on the pads and rotors (majority of the time, it is on the box). However, if the pads or rotors do not state anything about a break-in procedure, having some kind of break-in procedure done is still highly beneficial. A universal break-in procedure is to just drive the vehicle for 500 to 700 miles of moderate driving. During first initial 500-700, the vehicle should avoid heavy (aggressive) braking.