<p>As long as the question is on-topic, not duplicate and well posed, answering with comments is a bad practice, because it can leave the post officially unanswered, which is bad for our site statistics. Also, the comment can't be voted down (likewise, if it is a correct answer the author will not receive credits for it; which is also bad). Moreover, regarding good content, an answer posted as comment will not have the visibility it would have if it was posted in the answer box, which is bad because future readers might overlook it.</p>

<p>There is always the possibility to expand the one line answer with an example, a complement covering other possible situations, etc. </p>

<p>Below, there are CV meta related questions which are worth reading:</p>

<ul>
<li><a href="https://stats.meta.stackexchange.com/questions/2641/etiquette-for-answering-old-questions-addressed-in-comments">Etiquette for answering old questions addressed in comments?</a></li>
<li><a href="https://stats.meta.stackexchange.com/questions/832/comments-that-are-actually-answers#comment2366_832">Comments that are actually answers</a></li>
</ul>

<p><strong>Edit</strong>: </p>

<p><a href="https://data.stackexchange.com/gis/query/983514/unanswered-questions-with-answers-in-comments-per-tag" rel="nofollow noreferrer">Here</a> is a query in Stack Exchange Data Explorer (SEDE) to help finding unanswered questions answered in comments (in this <a href="https://gis.meta.stackexchange.com/questions/5030/finding-questions-which-are-answered-in-comments/5031#5031">post</a> I write about options on how to proceed with them).</p>
