One thing I tell my students is something Bill Dixon, chief photographer at the Lawton Constitution, told me in May 1982: fill up the frame.
There are a lot of good reasons to fill up the frame. In 1982, you filled up the frame so you wouldn’t have to enlarge (“blow up”) the useful area of the image as much. Enlarging a photographic negative also enlarges its flaws, like grain and dust, so filling up the frame makes sense.
In the digital age, filling up the frame has the advantage of actually using the pixels for which we paid so dearly. We were sold on pixels for years: “You need at least eight megapixels if you want to…” blah blah blah. So we’d buy an eight megapixel camera and immediately, and usually constantly, shoot images without filling up the frame, then crop out literally millions of those expensive pixels.
Possibly even more significant than the concept of preserving quality is the notion of preserving composition, particularly those often very-descriptive near/far relationships that help draw our viewers into the stories we hope to tell with our images. Particularly when we shoot with wide-angle lenses, we create lines and frames that invite the audience in to our images. We do that by filling up the frame in a very exact way (ideally), when we shoot the image. If we shoot too loose, then crop, those lines and frames can break down pretty quickly.