Paint Protection Film
The technology of paint protection films could be said to have been perfected during the Viet Nam War, when they were used to coat and protect helicopter blades from flying debris that may degrade the blades and cause shattering in flight. The same applications were eventually transferred to cars for example protecting the cars paint and metal from flying debris such as dirt, dust, snow, ice, rain, insects and even bird poop. (more paint stain than physical damage)

But there are films that add functions other than simple impact protection. These films may look identical to simple paint protection films, being of the same thickness (.008 mil) and materials, but may cost a little more for its added purposes. Below are some generic examples of them.

Solar protection films

These are meant mainly to block out the suns harmful ultraviolet rays which cause paint and fabric to bleach and discolor. Most are tinted, designed to reflect the sunlight and reduce heat build-up in the cars interior. Aside from that, anti-UV films by controlling interior heat build-up enhance driving comfort, climate control and feeling of privacy inside the car.

There are transparent ones for use on front and back windshields (Laws permitting) and side windows if desired. Such products may also be used for paint protecting the cars exterior much like a fabric protector.

Colored films/Graphic Art

This type is not used widely, because the colored characteristic reduces somewhat the aesthetics of the cars paintwork. It changes the cars color a little. However, some car owners use them just for that: subtly changing the cars appearance while protecting it from UV and flying debris and adding more shine. It makes the car look unique but not much, perhaps expressing a hint of the maverick in the car owners personality. Since the films are easily peeled off when necessary, periodic replacement may be had, each time changing the appearance of the car itself.
More likely uses of these would be by business owners advertising their businesses and products and services or small graphic details on cars for personal taste.

Windshield protection films

These are similar films but designed primarily for windshield protection. The main uses are keeping the windshield from being scratched and damaged by flying objects through providing a buffer material prior to the glass pane, and keeping out excessive glare that may temporarily blind the driver. Flying objects such as hail, small stones, bird droppings, or perhaps a gas station attendants careless wiping may damage the windscreen, causing lines and scratches to be permanently marked on it. Such tiny marking reduce the drivers vision especially at certain angles from the sun. Using a windshield protection film will prevent such damage, and since the film is replaceable, much damaged films may simply be replaced to make the windshield new again.