The Snow Card is not as dangerous as the others normally, but it can be if left to roam long enough. Basically, it's power is simpyl to make it snow nonstop. This was proven in Episode 36 when more than three feet of snow was dumped onto Reidenton.
Li attempted to use his Fire magic at first, but the attempt failed in the long run. Through anger, Sakura summoned the Firey Card to melt all the snow and chase Snow's form. When summoned as a card, it causes snow to appear.
