Off Screen, 45° left

A panorama is a 360° vision around the viewer's point of view. This assumes that the global view around brings more meaning that the 60° view of an ordinary photo camera. The framing of this 60° photo camera is also a cut out in reality, assembling elements on the same surface, excluding elements out off frame. What is the peculiar truth of this exclusion? Why not decide, whatever I want to shoot, to frame 45° left instead of the original picture I planed to take?