This is most useful when you are renting or borrowing a car. If you don't check before you hop into the car, you need to physically exit the car and move it if you guessed incorrectly.
There's no real reason why you can't fill up a reasonably large car (I (in the UK) have a Ford Galaxy) on the 'wrong' side of the pumps. Sometimes you have to be a bit more careful about positioning, but most hoses are long enough.