I unplugged the cable for my '08 e92 and havent experience any major related problems and stealership hasnt said anything to me after many services. love the sound, and cant stand the oem setting since it sounds like a car with silencer on.
The only affect that i notice might be a problem is that the flap inside the exhaust might be sticky now since its been on the open position for 3 years. When I take my car in for service, I would plug the cable back in, and will hear the flip closing/opening during startup and its a pretty loud metal *clink* sound. differently louder then when it was new, and clean pipe. my guess, the flap has built up crap in there and causing it to make a louder then normal clink sound when running. either way, once i am done at service, i unplug it back once i drive out the stealership. been debuting if i should bring up the clink sound before my warrenty expires in 6months and get them to replace the flap..............