Sometimes an answer is useful, but rather off-topic or in other ways not applicable to OP's specific scenario. Maybe the answer is too general, maybe the question is somewhat localized (but not TOO localized that it should be closed), perhaps there was a slight misunderstanding between the two, etc.
In any case, the answer was deemed useful enough by some people that it has received a few upvotes, but obviously it could use a better home. That is, the answer would be a really good answer for a different question.
Let's say there no dupe.
What should be done in this case? Should a new question be asked to which the answer can be migrated? (If so, what's the protocol?) Should the answer be deleted altogether? (I've seen this happen, and honestly I don't think it's the most ideal solution)