If a wall is not square or plumb, it will show up.

If a hallway is ¾ of an inch out of square, this will show up when the floor tile is installed. If window and door openings are not sized properly and at the appropriate elevations, it will cause problems with the installation of those items and affect the final appearance of a home.

Have you ever seen a roof drain centered above the front door? There is no substitute for paying close attention during the framing stage.