I can say on snow and ice it wouldn't help if the AWD is working properly.
correct. If working properly.
But if there is a large delay, it can be dangerous on snow/ice.
I've experienced white knuckle situations in the old 4eat equipped turbo GL. While negotiationg a turn, it would begin to "push" through the corner, front wheels start spinning just a bit and WHAM!!! the rear drive kicks in and send the car into an oversteer skid. Very abrupt and unsettleing.
In that case, I would recommend using the LOCK switch in very slick conditions.
Again, I have no problem with my newer, current cars with AWD working proper.