It is part of the main gameplay loop. In order to keep your car in a state where it protects you and is reasonably driveable, you must gather materials to craft repair items and replacement parts, in order to maintain the car’s panels, doors, and bumpers (which together function as armor), its wheels (which are necessary to get anywhere), and the various add-on systems you can craft for it. Tools gradually break with use, so you’ll also craft replacement tools, which are mostly for scavenging materials or interacting with stuff in the Zone.

By collecting a certain resource you gradually unlock upgraded parts and tools for crafting, which is the main way player power progresses during the game.