The front of your car takes the brunt of the road debris that assaults your car on a daily basis. Stones and road particles can kick up year-round. In the winter, you have to contend with the salt and cinders used to combat inclement weather, and in the summer the bugs can be just as bad.
Obviously, the stones and harder debris can chip your paint and expose the bare metal underneath, introducing the long-term potential for rust issues. But did you know that salt, chemicals and even bugs can eat away at the paint, eventually breaking it down and causing a similar potential for rust? This damage won't happen overnight, but that also means it might be so gradual that you don't notice until it's too late.
It's important to note that these products can only do so much to protect your car's paint. They might prevent damage from road debris and keep your paint safe in a parking mishap, but they won't offer any rigid protection against impacts hard enough to dent your car's body panels and fenders. Then again, most of the products that provide that kind of protection won't look good on smaller sedans, coupes and hatchbacks.