On the E90, E60 and beyond, its actually DSC Plus, that's why you have DTC.
DTC has two useful applications, one like mentioned by AB (in snowy/icy roads). Imagine if you at a traffic light junction and trying to take off, with the wheels spinning, DSC will intervene and you may get stucked.
Technically, let's say if the rear wheels are spinning 16% faster than the front, the electronics would intervened and cut off/reduced engine power and it the car still oversteers, individual braking will be applied, either front left/right depending on the corner direction.
Now with DTC switch on, the electronics will only intervened if the difference in wheel spin exceeds 20%. In our Malaysian context it means, more spirited driving around corners!!
Another feature of BMW's traction control system is DSC can be completely switched off. In the event you screwed up, just jammed the brakes and DSC would be activated automatically.