The term Pan/Crop comes from one of the editing techniques Sony Vegas users use to apply motion to the video by 'moving' the video around the canvas, creating a 'panning' effect. Most of the time a pooper will have a close up of a character's face, zoom in on it, or show the character from different angles. This trick may sometimes be used in order to point out an oddity, animation mistake, or something else.
It is possible in Sony Vegas to pan and rotate a clip so that it looks 3 dimensional. You can do this by setting the layer compositioning mode to 3-D Source Alpha. This technique can be used with other methods to create stunning visuals or landscapes for flash poopers.