When you apply the brakes, the rotors wear down along with the pads. Most of the Mercedes rotors barely have 3mm of wear allowed before they reach minimum thickness. From my experience with stock brakes, this is takes 2 sets of pads before the rotors are below min thickness.

For example, on my car, the rotors are 25mm new. Min thickness is 22.4mm (I think). After 1 set of pads, they were worn down to a hair over 23mm. Then pads got replaced and after the second set of pads, they were worn down to almost 21mm thick, which is well below min allowable thickness. At this point the rotors need to be replaced. There was no need to turn the rotors in between pad changes and if I had turned them, any extra material removed would have taken them almost to min thickness after 1 set of pads and made them essentially worthless. I believe at least on a C280, if you use a set of pads all the way down, then turn the rotors, you will not be able to use a second set of pads, the rotors will need to be tossed anyway.

Rotors are cheap and there is no practical benefit to turning them after 1 set of pads. After 2 sets of pads, they will probably need to be tossed no matter what.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record