I have several latex questions under my belt in SO, long before TeX SE was born. My question is - should we migrate old questions like these to their respective, more fitting, SE site? Pros for this are:
For starters, TeX wants your LaTeX questions. Seriously, they really do..
The best thing to do is do this on a case-by-case basis for different subjects and ask first. New sites not only are new, but they also develop all kinds of protocols, so make sure that not only is it acceptable to migrate, but also that you don't migrate stuff that will end up closed as off-topic or summat.
In a general scenario, remember that migration is primarily a tool to move questions that don't belong on the current site, not to move them to the more appropriate site. Super User still covers questions on Mac, Linux, and Ubuntu even though separate sites exist to address them individually. This is because ultimately cross-applicability makes the question fit on both Super User and the satellite site. However, any old iPhone or Android questions don't belong on Super User, and can be happily moved to the proper Apple and Android sites without any conflict.
That isn't to say you shouldn't migrate when there's cross-applicability. Sometimes the users of one community are fine with the migration of the stuff - try to see if there's a Meta question about it. Super User has a Meta thread specifically against migration to Apple and Ask Ubuntu, while the consensus here for Stack Overflow seems to be mostly fine with the migration of LaTeX. Other times, a question just truly is better addressed on the other site - we get some questions on Gaming about games on Ubuntu where the answer is so rooted in the Ubuntu architecture that migration helps all parties.
The only thing I'd note is to treat this not unlike mass retag or edit jobs - migrate in small patches. Don't make a flood of old content so large that it overwhelms all of the actual new content. Ask on the appropriate Metas about the viability of the movement, then do it slowly over time.
Remember the golden rule of migration:
Migration means “we want it”, not “let's shove it to them”.
In other words, you should migrate a question if think of the target site as “us” and you'd like the question on “your” site. Don't migrate a question if you think of the source site as “us” and of the target site as “them”.
Jeff's first rule of migration is a corollary:
Don't migrate crud.
Stack Overflow questions have often attracted answers that the more expert communities don't like so much. The target voting base is much smaller and often doesn't have the manpower to regulate the votes to better rate the questions (it would help if votes were reset upon migration.
If it's early in a site's beta, migrated questions can be disruptive because the target site hasn't fully decided on its limits. You don't want to migrate a question to a beta site only to have it declared off-topic after all.
If the site is already mature, there may well be a better-worded, better-answered duplicate on the target site already.
In practice, what that means is: do not mass-migrate questions to new sites. Do not migrate questions if you merely think “they” would be interested.
Ok, I've been repeatedly telling you not to migrate. But sometimes migrating a question can be a good thing. If you consider yourself a member of the target site's community, and you consider the question an especially valuable one for your site, and it's borderline or off-topic on SO, then flag it for migration (tell the moderator that you're to be trusted on your target site — being a moderator there would do it).
For new questions, you can lower the bar: migrate them if you think they'll get better answers on your site.
