It Can Reduce Harsh Sun Glare While Parked
On bright days, side mirrors can throw sharp flashes of sunlight. In some parking spots, that glare bounces straight into the cabin, toward nearby people, or even back toward your eyes when you return to the vehicle. It is not the biggest travel problem in the world, but it can be irritating.
Covering the mirror while parked can soften that reflection. This is more useful in open lots, desert roadsides, beach parking areas, or anywhere the sun sits low and strong. If your car is parked for a while, a bag can keep the mirror from acting like a small reflector.
But this is also where the warning matters most. Never drive with a bag over your side mirror to block sunlight. That creates a bigger danger than the glare itself because you lose the view behind and beside your car. Use sunglasses, sun visors, window tint that follows local rules, or simply adjust your position safely. The bag is a parking trick, not a driving trick. Before the engine starts, the bag comes off. No exceptions, no shortcuts. That one habit keeps the trick useful instead of risky.