Compositing allows a lot of choices, and a lot of control since everything is in layers. You can for instance blur a grainy sky and sharpen the foreground. In this case the foreground has a mosaic texture while other parts of the image are photo realistic. My model wore a hat for part of the shoot, but not this particular shot, so I borrowed the hat from another image. It’s not unusual to change the color of outfits, and I sometimes composite faces. Anything is possible.
When I do book covers I quite often do the full jacket to allow the author the option of printing. Just another perk.