It is worse than useless in the snow...
From experiment in the snow over the last couple of days if you turn it off it appears to ignore traction control type issues but still seems to give at least some correction if things become very squirrelly....
Having said all that, the car was pretty well behaved in tricky conditions - 0.5" - 1" of snow over sheet ice - in North Yorkshire on Thursday night and I managed to make it to the g/f's in the Yorkshire Dales when I was passing 4x4s abandoned at the side of the road...