If one question asks just about
A and another comes along and asks about
B, it can make sense to refocus one question to include the intersection and the other to exclude it. In that case, one question becomes
A and the other becomes
B ∖ A1:
If you happen to be quick about it, the answers separate naturally with the questions. If you aren't quick (or need to sleep on it figure out the best way to split the issues), you get a variety of answers that address
B. Thanks to editing, the system handles most of the cases. But it doesn't cover the situation where an answer to
A focuses entirely on the intersection of
B3. In that case, the answer collects votes, views, and comments on a question it partially answers and (after the questions are divided) it suddenly doesn't answer the question. A moderator can suggest a few things:
Delete the answer and copy it to the other question thereby losing the votes and comments.
Edit the answer to indicate that it was valid for a previous revision thereby exposing the unimportant details of site history to anyone who stumbles across it via Google.
Copy the answer to the other question and edit the initial answer to point to it thereby failing the same way as #2 and making voting, um, weird.
Do nothing thereby leaving an answer that does not answer the question.
What I propose is another option that will neatly solve all the problems we've created for ourselves:
5. Give ♦ moderators the power to move an answer from one question on the site to another.
I can think of other scenarios where moving an answer might be helpful besides the situation I describe above. If there are any traps that I might be missing, I'd love to know what they are, even if it's just hard to do in the SE code. I have to say that I assumed moderators could do this and so did one of our users. Since I couldn't find a related proposal that post-dated Improved Question Merging, I'm guessing it's just an oversight.