What is the physiological explanation for why we dream?

 During REM sleep the brain is activated and "warming its circuits" and is anticipating the sights, sounds and emotions of the waking state.

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.