Traditionally, the music software industry has approached stereo (and most recently "surround") sound by its data [as a grouping of mono channels or "tracks"] rather than by what its data represents [a stereo (or surround) "image" of a partial (or complete) sound environment - or "field"].  as an example, many commercial sound applications contain left/right amplitude meters which display the sound intensity contained on each channel, rather than display the actual perceived stereo image

however, it is often helpful during a mixing or post-production process to visualize the imaging of sounds within the stereo field of both recorded and synthesized stereo sounds - this imaging in the very least is comprised of both direction and breadth.  (with verisimiliar sound fields, all elements have some width, there are no point sources in the real world) - hence: f  i  el d    e   r !