Oops, I meant to say resting your hand on the shift knob is bad. At least according to Rogue Engineering. I didn't know this:
Within the transmission itself, BMW has a specification of 0.004"-0.006" gap between each gear and the shifter rail in the transmission (for reference, a human hair is approximately 0.0035"). This gap allows for the transmission lubricant to acts as a barrier so that the shifter rail and gear are not directly touching, causing premature wearing of the gear (not syncros), shifter rail, or both.
When you make a 0.001" change at the shift knob and maintain pressure (like resting your hand on the shift knob while driving), the required 0.004"-0.006" gap is closed, preventing the lubricant to ride between the gear and shifter rail. Premature wear of the gear or shifter rail may hamper transmission shifting performance, gear engagement, or worse, require rebuilding or replacement of the transmission.