<p>Once links to the cross-site duplicates have been provided, there doesn't seem to be a pressing need to close the question if it's squarely on-topic at this site; potential answerers can now decide whether or not they want to write an answer in full cognizance of actual or potential answers elsewhere, as <a href="https://stats.meta.stackexchange.com/a/6056/17230">@mdewey's answer</a> points out. (The notion that a question should be on topic at one site only seems very dated now; plenty are on-topic at several without any need for &quot;tailoring&quot;.)<sup>†</sup></p>
<p>And once the OP's been informed of the cross-posting policy, shouldn't they be given the chance to decide on which site they want the question? It's perhaps a little heavy-handed to immediately decide for them.</p>
<p>Another issue that sometimes arises is that even a currently unanswered question is part way along to getting an answer—there are comments asking for clarification, edits in response to the clarification—&amp; it would be a shame to throw that work away.</p>
<p>All in all I feel it's better to deal with the flag by taking the opportunity to weed out poor questions &amp; to check on the OP's other posts (such flags are certainly helpful), &amp; otherwise just ensuring that the necessary links are there &amp; that the OP's now aware of the policy.<sup>‡</sup></p>
<p>† That's not to say we should jettison the policy: the consequences of allowing cross-site duplication <em>en masse</em> might still be unpalatable.</p>
<p>‡ A repetition, though, should be dealt with by closing/deleting the question.</p>
