It's a bit of fallacy - it can help in some more extreme conditions when the ground underneath isn't great. In the city, it isn't going to do much if anything.Let a bit of air out of the tyres before she sets off, bit more traction and grip ?
It's better to make sure there's suitable tread and to drive slower, smoothly, raise your gears (start in 2nd, don't have high revs) and extend braking distances.
The biggest issue people have is they try to drive as they typically do and push the brakes firmly as with normal conditions - this causes the car to slide.
Stopping distance in this weather could easily be 30m+ at 20mph, rather than 6-12m: drop the speed, use your gears and slowly apply the brakes until you stop.
The insurance companies are already seeing a huge spike in suspected collisions from their black box data!