This is the second time I see this happening.
I don't want to argue, or flag, on the quality and constructiveness of some other user's comments, but a few times I wrote a comment on a post and it disappeared (moderation???) without knowledge or notification. Personally, I won't think three to four times before commenting, and I think twice and re-read when answering.
I know that upvoted comments do not make rep score, but sometimes one likes to write a nice catch. Of course, in a plural context one must be extremely aware that borderline comments may have a negative impact on others.
Example 1: I can't exactly recall where, but once I did a sarcastic (!) comment about the Catholic Church. Not rude language, no unpronunciable wording, no offensive expressions, not accusation of anything. Just sarcasm. The question was something like "At immigration of country X, will they refuse me if I answer that I used drugs in the past?". I sarcastically commented something like "Cool, the Vatican City may choose to ban people who once happened to sleep with their unmarried partner".
When I came back a few days later, the comment disappeared. I
learned thought that soft sarcarsm to the Church may be unwelcome. I would have made more sarcastic comments if I didn't see that comment disappearing. I passed on it and continued: trying to use less sarcasm on my future comments.
With this example I underline that I'm not interested in reinstating a comment or discussing any sarcasm-related policy.
Example 2: on this answer I made a comment about the name of Buffalo city, actually I cited one of the most strange pearls of the English language:
Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo (the comment didn't have the link for purpose of mystery). It worked as people started to upvote. And I was happy with it.
Now that I went checking for votes, it is disappeared. Without a reason. Okay that it is not constructive (!), but maybe was just adding some pleasure to the conversation. And I do understand that humour is particularly subjective and must be used with caution in a multicultural context.
It would be nice to inform/warn the user when a comment is moderated.
Con: some people may start long arguments, or flames, with Meta or moderators about "why did you delete my innocent comment?". Can be a headache to the staff.
Pro: one can stop from be used to bad behaviour long before it's too late for their account not to be suspended. I.e. one "learns" early from innocent mistakes.