Never. Since I own an M3 with DCT and paddles I now know why.
Using the paddles in a lightning fast (DCT) shifting car with a usable rev range somewhere between 2000 and 8000 rpm is tremendous fun, I use the paddles all the time in the M3.
However in the 535d, the experience feels silly and very artificial. Because of the small usable rev range (1500-4000?) the motor management system keeps overruling the manual shifts. IMO the laidback nature of the diesel powertrain doesn't suit the manual mode.
Obviously, it could be a different story in a petrol F10.
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2004 e87 118d (ret.), 2007 e92 330d (ret.), 2007 e87 130i M-sport (ret.), 2009 e92 M3 (ret.), 2010 f10 535d M-sport (ret.), 2015 f10 M5 CP (ret.), 2017 f82 M4 CP (ret.)
2022 g26 i4 M50 & 2009 e70 X5 35d