I don't quite understand the 'screenshot' option because it offers two options (Save full page and Save visible) and in my opinion they do the same thing.
'Save visible' just saves what you can seen on your screen at that moment in time, whereas 'Save full page' will also save anything on the page that you can only see by scrolling the page - i.e. anything above or below the 'visible' portion of the page that you're currently viewing.