Lectern displays are all about branding. When a speaker walks up to the podium, the screen can flash his company or personal logo for the audience to see. It reinforces the identity of the person talking by associating it with a well-known name. If the display is big enough, it might even be used as a secondary screen for the presentation. It could show pertinent images in synchrony with a larger projection screen.
These displays are usually flat screen televisions using LCD technology or similar. They range in size from about 15 inches to 30 inches or even more. Lecterns that have them are more dynamic. They tend to attract more attention than those without one, thus helping the speaker in getting through to the audience. This increases the effectiveness of presentations especially if the speakers know how to maximize the tool.