Shooting from above a subject allows the viewer to feel superior to the subject or feel protective of the subject. It can also give the viewer the impression that they are the object of the attention of the subject in the photo, as though it was the viewer placed on a stage (like in the example photo below). If the stage or "place on a pedestal" effect is achieved, the viewer will often feel adversarial towards the subject.
When you shoot a photo from below a subject can make the viewer feel as though the subject is in control of a situation. The simple act of looking up at a subject/object can impart a loss of control or the idea that the object is unobtainable. This has been used in real world situations throughout history. For example, thrones are set higher than other chairs, judges sit on a podium, and executive desks are just a bit taller than normal desks. The low shooting angle can also give the illusion of being inside the frame if the angle is severe enough.
Like almost everything in photography, this goes back to our instinctual reactions to situations. In a forest of tall trees we feel small looking up. As a child we must obey our larger parents. Shooting with an upwards angle allows us to tap into this instinctive response.