Two channels create a stage. Pan positions place sounds along it, timing and level differences widen or narrow them, and the mix acquires geography: kick and bass anchored center, hats flickering at the edges, pads stretched across the whole width.
Engineers police the field for mono compatibility, since venues and phones collapse it, and out-of-phase width disappears entirely when they do. The vectorscope is the meter for exactly this.
Visually, the field is free spatial information most visualizers waste. Panned energy mapped to screen position makes the image agree with the room’s acoustics, a correspondence audiences feel without being told.