My initial reaction: That tag exists?!
Some reasons for burnination:
Code review isn't something SO does specifically; it is like you said, better suited for Code Review. Hopefully they're high quality code refactoring questions, and not just a literal "refactor this plz" request.
One could argue that it's beneficial; I mean, you learn a bit about how to refactor code, but it's only for that specific code base. Not just that, but there are books and tutorials out there on the subject as well.
Some reasons against burnination:
If one wants to ask pointed questions on how to refactor a specific piece of code, I wouldn't mind that as much.
If the question is in regards as to why a specific refactoring is appropriate, I don't mind that as much either.
It would take some looking to dive through this; it's not easy to take a
sledgehammer fire-breathing dragon-like thing to this tag until the questions are considered for migration, survival or closure.