Some things people have said are perfectly valid. Other things not so much. If you are going to go AFK for an extended period of time then by all means put it in your comment/take your flag down.
If a party leader has his panties in such a bunch that i can't even take a piss without having to put it in my search comment, then i would rather not take an invite from that person. It is those kinds of people that tried to tell me how to play Drk when the closest thing they had to a DD leveled at all was Pld.
If it is going to take you the same amount of time +/- 2-3 minutes to put the comment up, as you will be gone, then it is stupid and if you don't have patience for that then you are playing the wrong game.