Need? That's up to you. The first time I flat-towed my Sonic a rock kicked up to the upper corner of the windshield on the driver's side. Bt time I returned home it had spread to about a foot long crack. didn't cost me anything to replace the windshield in my state with my insurance, but the time to get it done is time away from work and money lost in my business. Next time I towed the Sonic I had a rock guard.
So are you feeling lucky? Do you?