If you’ve ever been driving along the highway and your nicely maintained windshield was greeted by a rock, chances are a mud flap would have stopping that from happening. When wheels rotate at high speeds, they eject things they drive over behind them.
So really, getting a mudflap is a very nice thing to do. For other drivers on the road, and your four wheeling friends if that’s how you plan to use them.
Lastly, paint chips from rocks are another common issue people have. And yes, these will help deflect those.