I often take something from a question, or an answer to a question and convert it to a new question rather than muddy up the waters by bringing up something that's not really related to the original question. But I also sometimes post a comment on a different topic which I think is related but not likely to go very far. As to answering a question with a question, that depends. If the OP either doesn't supply enough info or is unclear, I think it's fine to ask for clarification. Likewise if you wan't to find out what the OP has already tried or checked. Asking an unrelated question is not good, but what can you do? As Dale says, give advice or ignore seems to be the best way to go in that case.