are a useful motivational addition to any information system.
Do systems need displays? Maybe not! Can you ignore the fact that it could be an invaluable addition?
I don't think so!
What are they? Simply put, they are devices for showing something to anyone looking at them. Weather it's relevant to the person viewing it depends on why and what the viewer is looking at it for!
It all boils down to the simple fact that people generally look at a display for either or both of two underlying reasons, These being for information and/or entertainment purposes.
We'll focus on the information reason for the time being, this being the one I know more about. We'll get to the entertainment side of thing later on.