There is a reason behind each one that gets deleted: To avoid an endless comment exchange that should be taken to chat, for example, or generally because they become obsolete, like "upload a picture" "done" "thanks". Comments are meant to be used for clarification or to add relevant information. 

Of course there is benefit in deleting them, most are like the ones above. **We get new comments all the time**, to new and old questions. Old questions don't get bumped, so those comments - lots of spam too - if lucky, are automatically flagged as low quality and we get notified. We (mods) get around 20 flags per day, most are comments. 

In reference to your [answer][1] to my other meta question, some comments were deleted in [this one here][3], and as I wrote in your answer, that exchange was turning into a flame war - Citing: the first comment, your comment, started with "thanks for the laugh". Then it got progressively passive-aggressive. A mod deleted them. 

I don't mind sharing the details of each deleted comment. I think very well about them before I delete them, I only do it it it will benefit the question and the site. I think all mods in SE have similar numbers on edits and deletions. I delete and edit a lot so I take responsibility.

I visit the site each day and spend a long time reviewing, editing, leaving comments and when I can, answering. If you [go through my log][4] and feel I have edited too much, I am more than willing to review those comments and adjust my deleting. 

But if I am doing too much pruning, I will have to repeat myself that **moderation should be about doing as little as possible.** When I visit SO I go straight for the answers and look at the comments for clarification, exceptions and such. We do design, so maybe we should allow more 'noise' in comments. 

**I think we need another meta post for guides on when to delete comments.** 


 [1]: http://meta.graphicdesign.stackexchange.com/questions/945/what-do-do-with-on-hold-questions-that-have-positive-votes-and-multiple-answers/946?noredirect=1#comment2721_946
 [2]: http://meta.graphicdesign.stackexchange.com/questions/945/what-do-do-with-on-hold-questions-that-have-positive-votes-and-multiple-answers
 [3]: http://graphicdesign.stackexchange.com/questions/29681/do-interfaces-really-need-to-look-good
 [4]: https://docs.google.com/document/d/1GDseq-kHkz2zUl4ukwPI7OJ_1ndTV7hmAtxMzY4JRX4/edit