I often come across "bad" answers ("not an answer" or LQ answer), that already have a canned comment.  Those comments typically come from one of two places.  

 - One is the LQP review queue, where you can select a canned comment when you vote to recommend deletion.  

 - The other is the Auto-Comment browser add-in, which allows you to add a similar comment to any post to explain what the poster did wrong.  People sometimes use it in conjunction with a moderator flag, and sometimes use it just to advise the poster about a problem (and they may wait to give the poster an opportunity to improve the answer before flagging it).

Sometimes, it's a good bet that the answer has already been voted/flagged.  Other times, it isn't clear.  I'm wondering whether I should mod-flag an answer that is probably already in the review-for-deletion process.

 - If an answer was identified by the system bot as low quality, it already has a pathway to the 20K queue, where users other than moderators can deal with it.  Do subsequent moderator flags get treated as additional votes to send it to the 20K queue, or do they put the answer in the moderator queue (losing the benefit of the 20K queue)?

 - Does the system do any kind of useful aggregation with flags, so adding my flag provides some form of input to the moderators that multiple people have flagged the answer (an indication that it might be a fast disposition)?

 - Does it serve no useful purpose, and possibly add unnecessarily to the moderator workload?