Turning the rotors isn't recommended, which is why the surface finish matters so much. If it is good, they can be reused, if it isn't (and would otherwise require turning) they get replaced.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue