We seem to get a lot of questions here that have a photography element to them, and considering that preservation of photographs and photographing records without destroying or damaging them is a major concern, I advise caution in these cases. opting to try to make the post fit before migrating it away.
Migrations should really only occur when the following has happened:
The question is closed as off-topic on the source site. In general, a question shouldn't be migrated to another site unless it's first deemed to be off-topic on the source site.
The question, although off-topic, is of a high quality, both in constructiveness and in providing plenty of detail. The question is about a real problem being faced.
The moderators discuss with the target community to see if the question is on topic there, and if it is, they migrate it. This also gives the community a chance to fix the problem.
If the question doesn't meet the above criteria, then it should just be closed as off-topic.
Thus, if a question can fit Genealogy SE or if it can be edited to fit Genealogy SE, it shouldn't be migrated away. In fact, many Stack Exchange sites share a heathy overlap. Just because a question is on-topic somewhere else doesn't automatically make it off-topic here.
My advice to moderators is this: If you think something should be migrated, post a link in the chat. You can also leave a comment on the post that you aren't sure the question 100% fits the scope. This will give the community time to weigh in and discuss alternatives before irrevocably kicking something out of the community. This gives people a chance to fix whatever problem exists with the post, and a chance to add value to this community. Hope this helps! :)
With that said, the rationale for migrating an off-topic question to another site is to give that question a chance to get good answers.