I use a plastic garbage bag or two. I want to minimize salt on my metal edges and the edges of others. It's really noticeable on long drives. Your edges without cover will be rusty. If it's a really short drive I won't bother. Anything over 30min. or roads that will be really salty and I cover.
Salt and water accelerates corrosion. If you don't want it on long trips, many short trips will do the same damage.