Using a dolly moves the camera horizontally in a shot. The best you can do with
a stationary (tripod mounted) camera, is pan across the scene. Dollying suggests depth because the size and perspective of objects in the scene change and move in relation to each other. Zooming - often overused by the amateur videographer - simply changes the size of an image.
Dolly shots can be very effective to follow a moving subject,
such as a person walking along and talking to a friend or
to the camera. Like jib (crane) shots, these dynamic views add great value
to a video production.