I have recently asked this question and received some comments.
The whole initial series of comments was removed by a moderator and replaced with:
Comments deleted. Comments are for providing constructive criticism on the question itself. They are not for answering the question. If you would like to answer, please write a proper answer which adheres to our quality standards
Why would a comment giving a quick answer should be deleted? It can be useful for other persons to have a quick start in giving an actual answer.
Also, going slightly off-topic can also add some fun flavor to the site experience. E.g. The most upvoted comment for this question is not "providing constructive criticism" to the question itself (which is not fit for the site), yet it is a very good one (it surely made my day).
My suggestion is to allow a slight deviation on comments admission policy as long as they are "nearly ontopic" and obey "Be nice policy". Reasons:
- pleasant experience - a little fun can do no harm
- can help - some users may be inspired by information in the comments and provide interesting answers
Also, StackOverlow users are used to such a policy (I have never seen a comment to be removed on any ofmy questions/answers).