Next is air quality. With the window closed, you are exposed to all the particles in your car, some of which (like food bits) can grow mold. If you vacuum up those crumbs, you keep yourself healthier.
Third, the dust in your car can slowly buildup on your windows. This reduces visibility. Cleaning out your care reduces, and potentially eliminates that interior buildup.
Finally, your car vacuum can do double duty. Besides cleaning your vehicle’s interior, you can use it in your home for small areas.