Once you've used the app once, payment becomes quite frictionless with an app. Without the app, I need to locate the pay station. Wait for anyone ahead of me already at the pay station. Then determine if it's the old type that issues a paper window ticket or the newer type that uses your license plate. If it's the new type, I have to enter my license plate info, taking care to remember not to transpose the two digits that always trip me up. If it's the old type, I have to wait for the ticket to print then return to my vehicle and place it in the proper spot in my door window sill taking care not to let it fall out when I close the door. Then I have to remember what time I need to move my car or add more time and return to the pay station to do so.
With the app, I have to do all of that once and the app remembers everything for me. If I am driving my wife's car, I don't have to try to remember her plate number. I can pay for my parking while walking to wherever I am going and I'll get a notification 5 minutes before my payment expires and can add time right where I stand at that moment. Parking apps can be great though it is annoying that every town seems to have their own app or payment provider.