Ah. I'll try my best to explain! I uploaded a smaller background, and it positioned it to the right side of the screen. In that case, I would have liked (it's definitely not a need!) to reposition my background image to the center, or to make it larger to fit more of the screen. Does that make sense?
Alternatively, even if it's set to fit all on the screen, users may want the option to be able to show only a portion of the background image. That's just what I'm thinking, but again, it's not like this is essential.