Here are sample photos of people riding bicycles. Each is shot by a different method, each with a different result. I shot the first image with a fast shutter speed. Both cyclist and background are crisp.
I shot the second with a slower shutter speed (1/160) and moved the camera in sync with the cyclist as I released the shutter. There’s a certain amount of luck involved in doing this, but when it works, the cyclist appears crisp while the background is blurred. It’s possible to achieve the same effect with photo-editing software, but why bother if you can do it in camera.
You can use a slower shutter speed but hold the camera stationary. This produces the opposite effect. The background is crisp and the cyclist is blurred. I supposed it’s all a matter of emphasis: a blurred cyclist is fine when she’s incidental to the image.
Finally, an image where the cyclist is more obviously incidental. Both cyclist and background are blurred while something else altogether demands our attention.