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We use our zooms to frame our subject.
We see a scene like the one below, and we zoom in if need be.

Original

What We Want in the Frame

Cropped version
That's great.
But our zooms do much more.
Many photographers are missing out.
Because we no longer have to carry around an assortment of fixed-focal length (non-zoom) lenses—we're less likely to learn how different focal lengths can be used.
As we zoom in and out, we don't have to pay attention to the focal length that we're using.
We're not putting an 85mm lens on the camera, and then deciding it's not right, and switching it for a 100mm lens.
We're just zooming in and out.
Compare the two versions of the birch tree scene below.

18mm - Wide Angle

70mm - Telephoto
Look at the backgrounds.
The wide-angle focal length pushes it back.
The telephoto focal length pulls the background closer.
This pushing and pulling of the background is useful.
Look at the volume.
In the wide-angle photograph, the birch tree is coming out of the photograph.
The telephoto focal length decreases the volume of the scene.
Often, telephoto focal lengths are said to compress scenes.
So, focal length is actually three tools:
1) Framing
2) Background manipulation
3) Volume manipulation
Use all three for better photographs.