Salt is an unwelcome type of contamination on your vehicle. Salt can cause rapid corrosion and extreme dage to unprotected metals. It can also severely stain polished metals and create a matte look over the surface.
Frost or ice on your windscreen can affect your ability to properly see your surroundings. Removing ice or frost from glass will increase not only your own safety, but also that of others. It can also be illegal to drive without proper visibility.