Yesterday, I received a private mod message because I was being chatty in comments and that I should stop doing that. The message was also implying that I did not know how to use comment properly.
It was true. Even though I didn't think I was doing something wrong at the time, I then realized that I was being chatty and that I definitively did not know how to use comment properly on this site (even though I usually have no issue knowing when I should post a question/answer or not on this specific site).
I then talked about this in chat and discovered that, even though moderators can now lock comments under a post (question or answer), they cannot comment-ban someone. If some mods really want to prevent a specific user from posting comments, all they can do is "regularly" ban them (so the user won't be able to post any question, answer or comment).
According to the mod I talked to in chat and some digging I did (eg: reading this answer), people really rarely get suspended for being chatty. Instead, most of the time, the person being chatty keep posting chatty comments while mod silently deletes them. Sometimes (like in my case), a mod will send a private message asking the user to please, stop being chatty. And, if the user is really, really annoying with all the chatty comment then they might "finally" be banned after a long time of "I post chatty comments and nothing bad happens to me".
So, quoting Shog9 answer:
From a user's perspective, they get absolutely no pushback at all until suddenly all of their privileges are gone... And on larger sites where comments can readily go unnoticed, this may take months or even years.
This leads me to ask for this feature:
Can we allow mods to comment-ban someone which would allow a person to still post questions and answers while preventing them from posting useless, chatty comments?
PS: Here are two related feature-request about comment ban, but those are for auto-ban by the system and not ban decided by mod: