One of the big selling points of high resolution cameras like the Nikon D810 and Canon 5DS are the ability to “crop in post”. Typically when people say this, though, they mean their lenses aren’t long enough and they want to be able to crop into the detail. Or, they’re tracking a moving subject that would be difficult to follow if they were trying to fill the frame.
But there’s more to cropping than just closing in on a small part of the image. Many cameras today are a 3:2 aspect ratio. Some mirrorless ones are 4:3. But there are so many more formats out there that give a different look and feel to your final shot. This video from Craig Roberts at e6 talks us through where they come from, and what they can imply to the viewer.