The benefit of a spiral descent is that you can increase the G loading which helps keep the speed down due to increased drag while maintaining a high descent rate. Airliners don't have very big G limits to start with and the passengers would find it particularly unnerving. I think the negatives would far outweigh the minimal benefits. The only real likely reason for an emergency descent is a pressurisation problem and the pilots have adequate oxygen to allow for a descent in straight flight. Having said that, it is sometimes advisable to turn off the airway so you don't conflict with traffic at lower levels but that would just be a single 90 deg turn, not a spiral descent. Also in an airliner you are typically wanting to get somewhere, a spiral descent doesn't get you any closer to your destination.
Edit: It was many years ago now, but I remember the CPL spiral descent essentially being a handling exercise, I can't recall it having any particular purpose.