One thing about BMW rotors is they don’t rust after 10 years on the car in the Northeast. They came from the factory with a zinc coating.
A GM rotor has the same appearance but was baked in nitrogen. It rusts in about 3 years.
So I would wonder when a person cuts the rotor, there would be a possibility of introducing a lip. Because the pads cut the zinc coating off the new rotor, so only the swept part is exposed.
Contrast this to a Lexus or Infiniti. I call it a (rust) stripe of shame. They all have large lips where the pads don’t sweep.
My .02.
Most people must not bother, but I’m peeping at rotors in parking lots and noting who got the $600 Midas aftermarket job with $29 rotors and who has OE