It becomes the 4 mirror when backing up, its that simple
In the summer i pull the truck straight into the garage, but in the winter I got a plow on it and I need it to line up just about perfect to get everything to fit and still be able to get in and out of both cars
That's where the target comes in
As for lining up trailers...only if the person who designed the car isn't retarded
I had a back up cam on my CX9, and it was offset
Which means if I backed up to a trailer, with the neck of the trailer dead center in the screen, it would be 8 inches to the left of the towball