That isn't strictly true with moving forward into a car park slot where you don?t actually need to see the front corners of your car, just how close the part of the car you may run into is to that corner of your car. Same with backing when deciding how close what is behind you is.
If the reference object is low down, you
But not necessarily stuff that is on the floor and not visible without a camera. Yes, you don?t have to put stuff there, but if you have a decent set of cameras you would be able to put stuff there, even if only temporarily because you plan to put it in the boot when you back in next time etc.
You don?t always need to, all you need to know if you are about to hit it.
And to see stuff that is on the floor in the garage that isn't high enough to be seen by the driver when the car is close to it.