<p><strong>I agree with @NickCox that as a general policy answer edits should only be "minor" (<a href="https://en.wikipedia.org/wiki/Copy_editing" rel="nofollow noreferrer">copy editing</a>),</strong> i.e. improve grammar, fix spelling and LaTeX mistakes, format the quotes and code blocks, insert full references and hyperlinks to papers, etc.</p>

<p>Substantial (major) changes should not be made via edits; if you think that an answer is incorrect or not entirely correct, consider downvoting, and/or commenting, and/or posting an alternative answer.</p>

<p><strong>However, I have encountered some situations where I think it is justified (with extreme care!) to violate this rule.</strong> For example, if a highly upvoted / accepted answer in a popular thread contains some sloppiness or misinformation and if the answerer is not with us anymore or simply does not react to the comments, it might be worth to edit. It is practically impossible for a new answer in such a thread to get more upvotes than an existing popular answer; and there might be so many comments already present that a new comment would not be very noticeable.</p>

<p>I did it a couple of times, e.g. with the accepted answer here: <a href="https://stats.stackexchange.com/questions/222">What are principal component scores?</a></p>

<p>Very rarely I have even decided to edit to improve an answer that was correct but I felt could be extended or clarified. E.g. the accepted answer here: <a href="https://stats.stackexchange.com/questions/53">PCA on correlation or covariance?</a></p>

<p><strong>That said, I re-iterate: I do agree that our policy should remain that such edits are generally not allowed.</strong></p>
