I would say too, that when your car is stopped and only 1 tire has good traction, then XI would work well.
I had a case on my old e46 where the car "sat" on deep snow and the rear wheels didn't get any traction. I think in those conditions, it would have helped to have XI as I'd have all the wheels pulling the car.
Also AWD can kind of pull you through your turn if its slippery, while for RWD, you have to ease through it, and be a bit more gentle.
Current: F87 M2 MT, E84 PP SP LP
Previous: F30 - 335i AT, E90 - 335xi MT, E90 - 330i MT, E46 - 330i MT