I'm in favour of such questions. Lately I've been doing research on teaching second languages, with a focus on French in Ontario, and have found some interesting articles suggesting that an effective strategy is not to rely on form-focused instruction alone, nor on a student's absorption of rules given a glut of content, but a mix of the two: look at content but include an explicit "noticing" component, in which the student's attention is guided to something salient or important. If a student independently identifies something as interesting or perplexing in some content, they're probably trying (and ready) to accommodate that new knowledge into their current schema.
Someone might object: "So it's useful to the OP. Is it useful to anyone else?" But I would say that making that assumption is the core principle of the Stack Exchange system, and it's borne out again and again every day. Very rarely does a concept only apply in only one case of interest to only one person.
Of course, the caveat is that it's only a useful question if the usage is at least a little opaque or interesting compared with what one reads about it in the average grammar book.
For example, say a person has read the basics on direct object pronouns and has seen standard examples like this:
Ta pomme ? Désolé, je l'ai mangée ce matin ...
This example of l' follows the general rules to a T; there's nothing unique about it. If a person asks about this sentence, the only viable answers are probably to reteach the grammar or to point the asker to existing resources or previous questions. So it's not very useful.
But if you come across this sentence:
Comme tu le sais, c'est un beau gosse.
Here it's not immediately obvious to an Anglophone or anyone who's read only a basic resource why this sentence needs le. Compare: "As you know, he's a good-looking guy." If a person asked about this sentence, the answer might draw on an insight that's not in every resource: French seems to construe the second clause as the object of sais in some deeper structure, and does this regularly across a lot of patterns. (At least, that's how I would tend to answer it.)
Q: How do I know whether my sentence is exceptional?
A: The important thing is to show your thinking. "I read about X, but here I see Y. Why is that?"
In my experience these questions are fruitful.