Underseal is protection from rust and corrosion.
If your car is exposed to humid weather conditions or stone chips, this requires a high-quality undersealing. When the car is new, it is vital to be foresighted with undersealing. The undercarriage is extremely exposed, and if the surface is damaged rust is imminent. Stone chips, snow, sleet, and the humid British weather are all factors that can damage the undercarriage coating.