Do moderators do this once in a while when they are in the mood or are some comments removed automatically?
The comment was not vital. I just need to know what to expect.
Your comment with the other comments all deleted was no longer needed. It was flagged as such which is why I deleted it in agreement with the flag in context.
We do regularly remove comments which no longer have value and are not needed anymore. This happens frequently especially moreso when there are flags against such comments.
The privilege to flag comments, posts, etc. is achieved once you get 15 reputation points.