It's another example of the shambles that is PPL flying. The flying school makes low margins and therefore can't really afford to not charge for time used as a general rule but your whole exercise needs to be repeated - so you pay twice but have the "experience."
If you hired a car that got half way to where you wanted, you wouldn't pay for it but flying breaks the rules and like you said, you don't want an argument when there's more business needed.