for me it wakes me the f up. It's strong like having drunk coffee or something. Results may vary of course, but works wonders for me and my focus during the day.

I know of an old woman who's beed ice-cold bucketing for years and looks great and hasn't been sick in a long time. Does this with -20C outside too. Yet I find I may get sick easier if it's too cold outside and I go all out freezing shower.