Assuming it's designed like everything else in modern cars, they're open in certain places and closed in others in order to give the system adequate air flow while also not allowing too much air in the engine bay or in certain areas.. Allowing air to go in to the wrong place could cause turbulence in the engine bay that would unsettle the front of the car, or too much air might add more air resistance and affect your fuel economy 🤷🏼♂️
When I had my civic, I data logged my intake air temp, coolant temp, system voltage and avg fuel economy with a scangauge2 because I added clear plastic behind the grill, cut to fit so it looked factory but blocked air into the engine bay. This was only during winter in Detroit, in order to facilitate the motor getting to operating temp faster, increasing my fuel efficiency and giving me faster heat from the climate system, as well as keeping the bay warmer as the car sits (meaning it doesn't get fully cold if I'm getting back in in 15min from the grocery). The scangauge2 was to make sure I don't force the system to run too hot, which would cause the cooling fans to kick on, resulting in a drop in fuel efficiency. I would often remove one side temporarily if it was going to be warmer that day