You get your car detailed—or even washed, for that matter—for the same reason you comb your hair or wear a clean shirt: to look good.

Detailing shops and carwashes might also claim they preserve your vehicle’s finish. But having a car detailed—or washed—is not like changing engine oil. Don’t change the oil and your wheels’ days are numbered; don’t detail the car—or even wash it—and you might lose a little resale value down the line, but probably not even that much.

Rust used to be one main reason cars got junked, but automakers now build corrosion protection into body panels and undercarriages or, increasingly, use high-strength plastics. Today, exterior components outlast the engine and other systems.

Neither the International Carwash Association, which represents professional carwashers and detailers, nor the manufacturers of carwash and detailing products can present hard evidence that detailing—or even washing—does much to prevent corrosion or adds much to the life of the finish. When you sell your car, the slightly higher price you’ll receive thanks to regular washing and periodic detailing is not likely to offset the cost of even two or three detailing jobs.

On the other hand, a good detailing job can do even more for the appearance of your vehicle than a new wardrobe and new haircut can do for you. Plus, cleaning your car’s carpet and upholstery can reduce or eliminate odors and, by removing dust and mites, reduce the discomfort of any allergy sufferers who might ride in it.

If you want a professional detail, our ratings of shops for quality and price should help you find the best.