Wiring is essential to make sure that the brain of your vehicle (ECU) can communicate with the different areas that need the information. Communicating to your cooling, fuel, or analytics systems will help your engine run most efficiently. You'll find that much of the wiring that comes stock with your car may not serve a purpose to you later if you choose to delete or remove components, which is where tucking and trimming those harnesses will help you shed some weight and space.