Motion blur can enhance the realism of a rendered animation by simulating the way a real-world camera works. A camera has a shutter speed, and if significant movement occurs during the time the shutter is open, the image on film is blurred.
Above: Scene motion blur creates an effect of movement. (The background is blurred because of slow camera panning.)
Below: The same scene with no blurring
3ds Max provides several ways to generate motion blur. Scene motion blur is one. Image motion blur is another. For most purposes, image motion blur or multi-pass motion blur give better results than scene motion blur. Use scene motion blur whenever you want to strongly emphasize rapid motion. You can use both image and scene motion blur in the same rendering.
Below: The same scene with no blurring
(Another option, object motion blur, is not meant to simulate a camera, but to improve the rendered appearance of fast-moving objects.)
You apply scene motion blur in Video Post. It is one of the options for a Scene Event. In the Add or Edit Scene Event dialog, turn on Scene Motion Blur in the Scene Options group, and then adjust the parameters.
Scene motion blur creates trails behind all moving objects by rendering the entire scene at multiple time increments within each frame, and then creating the frame by compositing the multiple images together.