Lets say a person asks a question that is on its way to being closed. For simplicity, let's say as off topic. Then someone answers a perfectly valid answer to the question as asked. Within the world of the question, it's a helpful answer. But within the site, it is not a helpful answer. Is it best practice to upvote such an answer as helpful, as it does answer the question?
This would apply equally to after the close-voting was finished and the question was closed.
I don't see a need to downvote the answer (if it isn't wrong), but answers to off-topic/unconstructive questions should not be encouraged as that encourages the questions themselves. So I usually just don't vote on it.
Folks naturally want to share an answer if they know it, human nature and all. It might not be a great question for the site, but it does show that there's a very friendly and helpful community here - I don't see the harm in them - vote however you feel comfortable but there's no reason to down-vote an answer just because it addresses an off-topic question.
I don't think we'll ever see a point where people take advantage of this - e.g. asking deliberately off-topic questions here because they know folks will answer them. It's nice if we send folks that arrived here by accident off with an answer, and direction on where they could get more information.
