Q:

Is it acceptable for a moderator to flag comments as "Obsolete"?

As described in A moderator flag on a comment silently deletes it even if the "other" option is selected, if a ♦ Moderator flags a comment as anything, the comment is immediately deleted.
I just saw a few comments on Cognitive Sciences which were obsolete: someone commented that a reference should be added, and the OP added a reference. Both have placed subsequent comments so I know these comments have been seen.
I flagged both comments as "obsolete" to auto-delete them and also leave a message in the log so my fellow mods would know what I did and why:
 
Is this acceptable? I ask because I also read this answer:

That said, if someone really wants to flag 500 posts and abuse their power to get a gold badge... more power to 'em, I guess, but their diamond and badge just might disappear

I really like my shiny ♦ so I'd like to keep it for a while :-)

A:

When you (as a moderator) delete a comment, or you flag a comment which is then automatically deleted, a log entry is created in the "most recent moderator's activity" view (admin/history/<moderator-id>), and in both the cases the entry is the same:

Comment deleted: [comment text]

If you just want to leave a log entry, both the actions has the same effect. 
It is true that, when you flag a comment, an entry is created in admin/posts/<post-id>/show-flags, but the reason you delete a comment (which is automatically done when a moderator flag a comment) is not an information normally useful to other moderators, and it is not given on users/flagged-posts/<user-id>, which would be the page where probably other moderators would look for having information about the bad behavior of the user.
Take the case you flag as not an answer something that should be written as comment, or that is a completely different question. In this case, you would provide more information to other moderators, who would be able to notice the user wrote X answers instead of commenting, or asking a different question, when looking at users/flagged-posts/<user-id>.
I am not saying that in one case is acceptable, and in the other one is not acceptable. I am saying that in one case you are not giving any helpful information to other users, while you are probably giving useful information in the other case. I imagine that knowing a user wrote X comments that were then obsolete is not an information useful for the moderators, as that is not a reason for banning a user from a site.

A:

Sounds like busywork to me, but hey, if you find it helpful, knock yourself out. 
Unlike post flags (WHICH YOU SHOULD NEVER, EVER ABUSE IN THIS FASHION), comment flags don't count against the author in any way, so the only one you're hurting is your button-clicking finger. 

