I am immediately reminded of the following phenomenon:

"Let's consider an elliptic curve $E$ over $\mathbf{Q}_p$."

~Speaker begins to draw a donut at the board~

Clearly this is wrong. The speaker may even mention how wrong it is. But there's enough of a kernel of truth to the picture where it may be helpful for the audience. Justifying why the picture is valid in the situation being considered would involve some hard and not undue model theory, but doing anything more than waving your hands and saying the magic words ("a-la-ca-Lefschetz!") is likely to derail your talk so badly as to effectively destroy it. Even if the picture is not completely valid for what you're talking about, it's a visual aid which is at least an easily described first approximation to the truth.