^Is the balloon sum the amount you havent paid yet, which you then still have to pay?
Have you not overall paid over and above for a car?^
I view it like this:
'Buy' a car and will have to put down a deposit, make monthly payments, and then sell it at the end.
PCP a car and you will have to put down a deposit, make monthly payments, but can then give it back after the agreed period if you don't want to pay the outstanding balloon payment - no hassle of selling it.
With a cheap car I'd just buy it outright, but people typically use PCP for new or nearly new cars.