A rock kicks up on the highway, and now you've got a chip that's about to become a crack. Windshield protection film is a clear layer over the glass that takes those impacts so the glass doesn't. It's the most common damage on a car that sees real miles, and the easiest to avoid.
You won't notice it's on there, and it won't distort your view. When it finally wears, replacing the film costs a fraction of an OEM windshield, especially one loaded with cameras and sensors that need recalibrating.
Good fit for highway commuters, track-day cars, and anyone who's replaced one windshield too many.