In this closed question, the comments were moved by @rob to a chat. I was not interested in chatting, I just wanted to make an observation on the question itself, so I wrote a comment, which I found was removed today, as if it were useless to the OP. The comment did not appear in the chat either.
What is the rule about this?
The "move comments to chat" button only works once. After that, comments can be deleted, but not moved.
When we move comments to chat, we'll sometimes rescue one or two comments that are especially helpful in clarifying the post they're attached to. Likewise, a comment that comes after a move-to-chat but is clearly helpful may stay around. But in general, on a post where people have gotten so chatty in the comments that the comments have been cleaned up once, a follow-up comment is likely to generate an additional discussion. And because people don't like to read long threads, especially with the modest barrier of a chat link, the resurrected discussion tends to have overlap with its predecessor.
I was not interested in chatting [...]
Don't let this stop you from using chat. There is no obligation to use chat "synchronously," where you keep the browser window with the chat room open and stare at it waiting for your correspondent to reply. If you step away from chat and get an @-reply, you'll get a notification in your Stack Exchange inbox just like if you'd gotten a comment reply. Feel free to ignore all of the real-time bells and whistles of chat, and treat it as a place to make comments without worrying (too much) about their number or their immediate or long-term usefulness.
What is the rule about this?
The rule is that, if you've written something and thought "I certainly would be annoyed if this disappeared," then a comment is the wrong place for it. This is independent of the move-to-chat schedule.
