My shop manual states: "carefully wear in the new brake pads by slowly braking from about 80 km/h to 40 km/h several times. Allow the brakes to cool down in between."
This sounds similar to the directions given with my old Saab 900 which stated to slow from 30mph to 10mph in about 5-10 seconds, then drive for about 1 minute, repeat 10 times. The idea is to burn off the chemicals in the adhesives that bind the brake pad materials together. If you don't, I guess it can leave residue on the rotors and pads that reduce braking efficiency.
Don't forget to put a little anti-squeel past on the back of each pad, a little high temp brake grease on the edge of the brake pad backing plate, and a little high temp brake grease on the spot were the retaining pins touch the anti-rattle clips (if your application has them). Wire brush the hub before you install the new rotors. Buildup on the hub can lead to warped rotors.
'84 300D, 173k
'90 300CE, 161k