A comparison may explain an unfamiliar quality (bayān al-ḥāl), establish its degree (bayān miqdār al-ḥāl), or make a surprising claim persuasive (taqrīr al-ḥāl).
A pleasing analogy can beautify its subject (tazyīn), while an unpleasant analogy can make a fault repellent (taqbīḥ). The formal kind of simile and its rhetorical purpose are separate dimensions; being mursal does not determine the purpose.