My pants don't have big enough pockets to carry enough change given the parking rates in California.

I like paying for parking with my phone. It lets me extend when the time is about to run out and cancel the remainder when I leave early.

Does cancelling refund the extra to your card? I assumed most systems would just eat it so I may as well leave it for the next guy.

Canceling refunds the extra amount to my balance. The app only charges the balance once a month.

You can't leave it for the next guy, because it's not a parking spot that's paid for. Instead, you pay to park a certain car in any spot in a larger parking zone.