I was wondering why some people uses comments to answer a question, instead of posting an answer.
I know that the easy answer would be "there's no reason, they're just doing it wrong", but I've seen people with high reputation doing this in some punctual questions, and I'm just curious about if there's any special case when a comment is better than an answer.
Here's an example of what I'm talking about. A user with more than 18k reputation makes what could be a detailed answer in the comments, instead of posting a new answer.
So, in which cases is it better to comment? Is there any unwritten rule I'm missing?