Have you ever uploaded a picture into your twitter feed and not been happy when the image is cropped, wiping off important information?
Often I see people upload pictures of books and two crucial items are missing from the cropped image - the full title of the book and the name of the author.
Of course, you can click on the image and you'll see the image in its entirety but you want it to be shown in it's entirety without having to click on it. The casual scroller looking down their twitter feed might not bother to click to see the full image. So it's a lost opportunity.