Camera panning is one of the most used cinematic techniques, and for good reason. It can make otherwise static shots more dynamic, give vistas a more expansive feel, and track the movement of a subject, among other benefits. However, results may appear unusual if the panning rate, settings and method are suboptimal.
The apparent panning speed is controlled by both the physical rotation of the camera, the camera’s sensor size, and the focal length of the lens. For the same on-screen effect, a camera needs to be rotated more slowly when using a smaller sensor or a longer focal length lens because smaller sensors or longer focal length lenses span a narrower angle of view.
Being able to control panning is important because moving too quickly can cause unpleasant visual artifacts. Objects or backgrounds may appear to flash across the screen in discrete jumps, for example, whenever the on-screen displacement is too great compared to the duration between frames. This is commonly referred to as strobing or "judder," and has happened since the early days of film.
See full details and examples of Panning Speeds in the RED 101 Article: Panning Speed Best Practices
Check out the interactive Panning Speed tool and more on the Cinematography Tools page.