The benefits of applying an undercoating to a car include rust protection and sound dampening. These benefits may be outweighed in many situations by the main drawback to undercoating, which is its cost. Depending on where drivers live, undercoating can significantly prolong the life of a car and keep it from suffering from rust damage.
Cars normally do not suffer from rust damage unless they are driven in areas where there is a high salt content in the air or in the ground. Driving in coastal areas or in areas where winters are long and significant amounts of salt are used on the roads can cause rust damage to develop quickly on the underside of vehicles that are not outfitted with undercoats.
Undercoating also offers some sound dampening benefits by reducing road noise. These benefits are minimal, since the undercoating is similar to paint in that it is sprayed on to the undercarriage of the vehicle, but drivers with noisy commutes are likely to notice the difference.
Drivers should keep in mind that undercoating can negatively affect a car's fuel efficiency. Adding additional weight to the vehicle, even if it's just a spray, may cause the vehicle to perform less efficiently.