The following touches and expands upon the "Lens Compression - Flattering Your Model With Focal Length" article. While that does a good job of showing the effects different focal length lenses have on a model when framed the same, it doesn't really mention backgrounds, the effect the lens has on it and how we can apply that to our photography.
Virtually all of us have a go-to or favourite lens that we inevitably end up gravitating towards. The reasons for this vary. Some will love a lens purely for it's sharpness, or way it renders facial features. Others for the shallow depth of field, or the flexibility a zoom lens offers. Your lens choice may also be governed by what you normally shoot. For example, if it's bugs and flowers then a macro lens will most likely be on the front of your camera. If you shoot portraits, maybe an 85mm prime. Birds and wildlife a 300mm+ lens. For those into action sports the 70-200mm f/2.8 is often the weapon of choice.
The common theme among all this is subject matter. How sharp we can get them, how aesthetically pleasing we can make them look and how isolated we can get them from their surroundings. The emphasis is solely upon what we are intending to shoot. But how many photographers consciously approach a photograph from the standpoint of the background? Very few I should imagine and yet it can make a huge difference to the image.
We know to avoid distracting elements in backdrops by either positioning our subject or ourselves so that it doesn't enter the frame. We'll deploy longer focal length lenses to blur busy backdrops into a creamy blend of bokeh. How much of the background we want rarely factors into the equation though and yet it could improve your photography dramatically. So often we here the words "make your subject as large in the frame as possible". To be fair, that is generally pretty decent advice. It puts emphasis upon our model and makes them more interesting. However, what about if we took a leaf from the environmental portraiture book and placed our subject in a scene that lends itself well to the portrait?
As mentioned at the start, lens choice has a big impact upon compression of a scene, as well as the angle of view. This is important when you have an eye-catching backdrop that you'd like to make part of your portrait photograph. I'll give you a scenario that most people can identify with - holiday snapshots. At some point in our lives we've had to deal with sitting through someone's holidays photos. Amongst all the pictures of tourist attractions and silly antics, there is invariably some landscape shots, which on the whole tend to be as boring as hell. You often hear "It was absolutely beautiful there. The pictures don't do it justice though."
The reason for this (aside from perhaps unfavourable weather/lighting conditions) is their focal length. The shooter thinks "Landscape shot. Better zoom out so I can fit it all in." So they go to the widest focal length on their camera and take a photo.
In doing so they have done one of the worst things often possible in landscape photography. That is to squeeze everything into the frame. The more you squeeze in, the smaller everything becomes, giving less impact to the viewer. Not only does it make everything smaller but it also sends everything further away. That lighthouse on the headland is now just a few pixels on the resulting image.
Conversely, if you shoot with a super-telephoto lens, you magnify everything, making it appear closer than it actually is. This is the compression effect of a lens. Think about it, why do you use a 300mm lens for photographing birds or wildlife? It's because it magnifies them, making your subject appear much bigger and closer in the viewfinder than they really are. What most people don't tend to realize is the exact same thing is happening to everything else in the image!
These attributes can completely transform the look and impact of an image. From including or excluding areas behind a model, creating greater or less seperation with the background, or compressing/expanding the background.