The advantage which I see using bitcoin as a payment method here for the parking is that if let's say you know you are going to exit the mall very soon, you can just initiate payment online half an hour or so before by just scanning the QR code to make the payment using your smartphone. After that proceed straight to the parking lot without wasting any time. Of course, that couldn't be easier
You could do that with fiat, though. Some benefits with BTC could be
1) lower cost for the consumer compared to forms of payment with high transaction fees.
*even this could be done in fiat if a debit card is used, except with BTC, you don't have to worry about being charged for insufficient funds like is common with banks.
2) no chargebacks (good for the parking business).
3) no currency conversion fees for ppl who switch countries and just want to use the same money as usual.