I think there are two situations with translation-for-assessment.
Asking a kid to translate a sentence or passage in writing, on a test, demonstrates that he can eventually get meaning out of it. I assume that if a kid can produce a correct English sentence that reflects the meaning of the Spanish (or whatever TL) sentence, that he does in fact understand, because for the purpose of this argument I’m assuming the kid is a native speaker of English. There is no comprehension load on a native speaker talking about familiar topics, which most of what is done in a K-12 language class will be.
Asking a kid to translate as a comprehension check during oral input demonstrates that he can immediately get meaning from the sounds coming in. To me that is a higher demonstration of comprehension, because there’s no time to think about it or puzzle it out.
But for my money, both are both legitimate and pretty much indispensable to know what’s going on “in there”.
The reason translation has a bad rap is the old practice of giving long translations of language that hasn’t been mastered yet for the purpose of learning that language. “Lines”. Old-style Latin classes. That sort of thing.