I explained to a customer that a model serves two functions:
1) Declarative / Documentary and 2) Interrogative / Investigative.

In the first case, one can ask questions like "How does this widget get from point A to point B?" or "What exactly is that fellow's job?" In the second, "What are the likely consequences of allocating resource X in this other way?" or "What happens if I route that material in this other direction?"

Even technically-minded people appreciate concise, lucid explanations. Your checks are in the mail.

tx,
tff