##TL;DR: Don't send bad questions to other sites.

That's about it. Each site has its own rules, its own preferences, and its own standards. It's important that any question you send to that site meets all of those requirements. If you don't know, won't fix, or don't care about that other site, **don't migrate the question**. Anything else is tantamount vandalism.

Take the following example.

> ###I hate Mint
> I installed it because a friend told me to but it's awful. lol.

That is off-topic here, so that means it's on-topic on U&L or Superuser, right? Would you migrate it? That is obviously a flagrant example, but you do occasionally see people forgetting this and trying to migrate some really awful posts.