You don't technically need it, it's just what you said. A shield. It protects all the parts underneath the car, including the engine. If you don't drive with one, you run the risk of stuff getting kicked up underneath or having something torn off. My engine shield got torn up last winter by big pieces of ice. Had I not had the cover, my engine could've gotten torn up instead. There are a few different pieces under there (3, I think?), so figure out what you need then go searching around. If you want the insurance, anyway.