Stereo systems build illusions. The better the stereo system, the more believable the illusion.
It's not something people think about a lot, yet it is one of the foundations of what we strive for. First time listeners to Music Room Two get a 5-minute explanation of what they are about to experience and why. Their reactions to that explanation are always guarded until the system begins to play. Then it's all grins.
The questions follow soon after. "The sound is coming from the front of the speaker, right? How is it possible the music appears behind the speakers?"
I was recently asked a very interesting question after the first time listener experienced the illusion of depth. "What's the value of depth and why does it change from recording to recording?" I answered his question by playing an example, the Mahler 3d.
"The system is attempting to reproduce the sound of as many as 100 musicians seated onstage in a very long hall," I explained. "Without proper depth, you'd get a scrunched up collection of horns and strings that would not sound right."
So while depth, width, height, and soundstage are only imagined, they are real enough to justify whatever means are necessary to achieve them.
The difficult part of this equation is understanding just how important electronics are in creating the magic trick.