Not bad, but probably not good. I do it often now myself, certainly a trade off of convenience for time.
I love my Volkl AC30s and want to maintain them for as long as possible but there are now other little packages to transport to and from the car and when on long weekend trips saves much time to just leave skis on the car.
Regular cleaning and waxing should prevent longer term damage associated with salt and sand. Think about this, while residual sand and salt probably is prevalent at road level, if you look on the top of your hood or roof after driving hours through a storm do you see visible granuals of dirt or salt? No, because of the aerodynamics of the vehicle and the fact that dirt and salt are heavy. Think about that. Yes, there is residual but nothing major me think.