A PCP will guarantee the minimum future value of your car, based on the annual mileage you choose.
This is a safety net that then allows you to budget for a regular change of car, regardless of how car values fluctuate.
At the end of the payment term you make the decision to either pay the final payment and keep the car, trade it in and upgrade for a new one or simply give it back to the finance company.
Whatever happens you are guaranteed not to have any negative equity.
Negative equity is when the amount you still owe the finance company is greater than the value of the vehicle. This is often found on 60 month term hire purchase and bank loan agreements.