Window tinting film for your car helps block out UV rays and gives you a little more privacy depending on how dark the film is. But very dark film also changes how well you can see through those windows, and that means you have to consider a few issues. Whether you're about to get window film or if you're bringing a car with film into another state, you have to be sure that you get the balance of privacy and security just right. None of these issues will prevent you from getting window film, but you might find that a lighter shade would work better for you.
Rear Dash Cams
If you use a rear dash cam to film whoever's behind you -- maybe you want to get evidence in case someone rear ends you -- the film won't prevent the camera from seeing through the back window during the day. However, at night, you'd need to do two things with the camera: enable night settings, if available, and increase the exposure, or EV. However you also need to consider how dark the film is. If you're looking at getting very dark film, test it out to be sure the camera can still see after you've enabled those extra settings. You might be able to get a sample piece from the shop that would install the film, so talk to the shop about getting help with that test.
This one applies to those who want to add very dark film to the rear door windows. If you're in the habit of checking your backseat before getting into the car to be sure no one's hiding there, again, you will need to check how well you can see in through the film-covered window when you open the door. Sometimes, if your car's cabin ceiling light is bright enough, there's enough light to let you see through. But again, test this -- you may want to look at films that aren't so dark instead. They'll still block many UV rays, if those were your reasons for getting the film.
New State Laws
If you already have film on your windows but are bringing your car in from another state, you should check to be sure that the level of darkness of the film you have is legal in your state. Levels vary because of privacy and safety reasons, and you might need to change the film to a lighter one. The film shops in the area will know the legal limit for each window.
The shop that will install the film is your best resource in these cases. See about getting samples or working out a way to test the film against your windows at the shop when it's dark out.