<p>This is a (lightly edited) composition of the comments left above by @Scortchi, @whuber, @Glen_b, and Roland (I am marking this answer as CW). I believe they fully answer this question.</p>
<blockquote>
<p>There is no practical distinction between &quot;focus on&quot; and &quot;about&quot;. Migration occurs when the question is likely to be considered on topic at the destination site. Closure occurs otherwise.</p>
<p>In practice we often close questions just because they're not good enough to migrate to SO. Many such lack a <a href="https://stackoverflow.com/help/mcve">minimal, complete, verifiable example</a>. Not every programming-related question is on topic at StackOverflow.</p>
<p>At the least be sure you're familiar with the requirements of their help/on-topic before trying to migrate there. If you don't feel qualified to judge if the question is of sufficient quality for the migration destination, then don't vote for migration.</p>
</blockquote>
