Why do people often do unnecessary things while performing a main task?
In the whole scheme of human consciousness, these movements may be a result of what one individual person's autonomic and central nervous system has been conditioned to expect. While awake during different hours of different days, implying different variables to be present depending on [social code] etc, our central nervous system (CNS) has a threshold for response- the level of response/arousal to sensory input accompanied by these variables stated above will ultimately help someone read what their basal level of arousal is. If that basal level arousal is not met in a certain social context (this basal level has increased via techna-cultural advancement) than the body may expend this energy via other methods of movement or concentration.