This question was closed as off topic, but was not migrated. I (incorrectly) decided to vote to close and migrate to Stack Overflow, but the question was not migrated for quality reasons.
I understand Jeff saying "don't migrate crap", but can someone actually give guidelines on when questions that could otherwise be migrated should simply be closed? This seems to be a point that close-voters tend to miss.
Per this question, there are other reasons why questions should not be migrated. For example, a question should not be migrated to a beta site unless the site has established itself. Can you list any other reasons for not migrating questions, in addition to low question quality? (This might be useful for users who flag to migrate.)