If you live in a snowy area do you need to have undercoating for your car?

I've always heard you did need this undercoating in cold snowy climates. Not to protect you from the snow, but to protect the car from the salt that is used on the roads. You also need this undercoat if you live on the coast, due to the salt from the ocean. I have also heard it is quite expensive to have this done to your car.