What a smart object does is wrap your layer in a container so that you're never editing the layer directly; instead, you're editing the container. When you rescale the container, you're not changing the dimensions or anything else about the photo; instead, you're changing the container in which it's contained, ensuring that the photograph always retains its original high resolution.

If you enjoy editing photos, guess what? You can turn that into an upsell. When you set up your photo editing services properly, you might not even need to shoot anymore — you just might trade in your camera to make a living as a photo editor.