If you have beautiful alloy wheels, or even just “okay looking” alloy wheels, they contribute massively to your car’s aesthetic appeal and are usually worth at least a few hundred dollars as an option.
Every time you tap the brakes, a little bit of black dust is emitted and most of it lands on the alloys. You may have noticed the front wheels of city-dwelling cars looking especially dark from constant braking in stop-and-go traffic. The effect is magnified in the event of a panic stop, and if you slammed your brakes on the highway your wheels might look like they had been sneezed on by a dragon (assuming soot accompanies all that fire breathing). This is unsightly if left unchecked, but worse, it can stain permanently and reduce the marketability of a car when you’re ready to sell.
Enthusiasts might swear by rim-cleaning products to extract maximum shine, but if you're willing to do it often, all you need is a damp rag to remove most harmful brake dust. Think of it like leaving food stuck in your teeth; unattractive in the short term and harmful if left for days.