If you see a terrible formulated question which is hard to understand(for example bad english grammar or whatever) or a duplicate but you do know the answer to the question, should you still answer the bad question? Or just leave it be?
If it's salvageable, i.e. You can edit it and it won't be close worthy, it's best if you salvage it, then answer it.
If it is a sure duplicate or cannot be salvaged, it's best if you didn't answer it, and instead educate the OP on why his question is about to be closed/deleted.
Remember, our goal is quality, helping out other users is nice but it is a secondary goal. Flooding the site with answered duplicates doesn't help anyone, half-assed questions getting low quality answers (because you can't really answer a question the truly deserves being closed) doesn't help either.