For clarifying a state, the purpose is to make the subject easier to understand. If the comparison model is itself more obscure to the audience, the simile may increase confusion rather than reduce it.
For establishing possibility, an apparently unlikely state is explained through an accepted analogous case. If that supposed model is equally unintelligible, it fails as a persuasive comparison.
The assessment of rhetorical success therefore begins by identifying the purpose, then asking whether this particular model genuinely advances it for the intended audience.