Sometimes I see a question that is clearly and indisputably off-topic (wether it's opinion-based or too broad etc.), and I vote to close the question for the appropriate reason. However, just because it's off-topic doesn't automatically mean it's a bad question. Every now and again I come across a very a good question that just happens to not be a good fit for SO, and sometimes I have in mind a good answer that I believe could truly help the OP.
My question is: is it bad to answer these questions, knowing they are indeed off-topic? I am perfectly aware that the question will likely be later closed/removed, but the OP will still likely benefit from the answer. I personally see no harm in answering these questions.