Parent question: Erasing comments for questionable reasons
I am trying to get a general policy. My initial concern was about comments to answers that asked for details and/or corrections, and were erased as soon as the answer was updated accordingly.
There are numerous comments all over SE that were asking for answers updates and were kept online even though the answer was updated. Personnally I think this is good for the question OP because this way they can keep track of answers evolution.
However, technically those comments are rendered useless by the updates. So they do fall under the flag category "no longer needed".