An insightful overview of teleprompter tips, sightings during the US presidential primaries can be seen here, at Garr Reynold’s site, Presentation Zen.
Teleprompters allow for speakers to present without the apparent use of notes. Keep in mind however, that there is a learning curve, and without preparation can appear to be more stilted or wooden than reading from visible notes. The teleprompter operator listens to the presenter and adjusts the speed of the words so they flow naturally. Additionally, this allows the presenter to ad-lib, or go off-script, without worrying about the script running away from them.