<p>Some topics that are now considered off-topic used to be tolerated in the early days of this site. Consequently, there exist old threads with lots of votes/views/answers that are off-topic under current standards. Our practice is to close such threads because keeping them open can send a wrong signal about what is currently on-topic. As @whuber wrote,</p>

<blockquote>
  <p>[this] has helped us respond to users who complain (sometimes very aggressively) that their off-topic questions should be left open because they are just like such-and-such a question from years ago.</p>
</blockquote>

<p><strong>There are two ways to close such old posts.</strong> One way is to close them as off-topic as usual. Another way is to "lock" them for "historical significance". Apparently, locking is preferred to closing -- see @whuber's and @Glen_b's comments under <a href="https://stats.meta.stackexchange.com/q/4791/28666">Should we close old, outdated and off-topic questions?</a></p>

<p>I don't know understand why this is the preferred way. I can see a number of disadvantages of locking:</p>

<ol>
<li>It can only be done via flagging, i.e. community cannot take care of locking without mods.</li>
<li>Similarly, it can only be undone via flagging, i.e. community cannot reverse a wrong decision without mods.</li>
<li>When a thread is locked, it's not possible to edit any answers, post new comments, or even vote on them. I.e. if there is a mistake in one of the answers, it's there forever, and one cannot even comment to point it out. Note that sometimes we are talking about very visible threads with large number of views.</li>
<li>The displayed message says that the thread is locked "for historical significance", but often there is no particular significance.</li>
</ol>

<p>So I see at least four disadvantages (#3 being pretty severe in my opinion), and not a single advantage. What am I missing?</p>
