C'mon. What's the point?
You flag yourself for PvP on a PvE server. But you aren't in the Plaguelands trying to capture towers. And you aren't in Silithus collecting dust. You're in Desolace killing skeletons.
There you are, level 36, Paladin, and you've flagged yourself. I suppose it guarantees you won't heal anyone, or be asked to heal, or buff, them. Is that your goal? To be anti-social? "I've infected myself with a lethal virus. You want no part of me." All you want to do is grind and be left alone, so you flag yourself?
You play on a PvE server by choice. I know I do. I played to 60, and into the end-game, on a PvP server. But I couldn't bear my wife dying at the hands of some punk Night Elf, or worse, Gnome, Rogue. So we transferred. So you rolled on a PvE (RP) server. And then you flag yourself.
Okay, I see some folks doing it in order to show they have balls of steel, or they're Warlocks. Who's going to mess with a Warlock. In fact I've seen a few flagged Pally's in the higher level areas. Who's going to kill a high level Pally? How? They'll heal to full twice, and you'll be bored to tears before you even get close. Meh. Not worth it. And Pally's have gotten sponge-worthy with the patches lately.
Anyway, seeing this level 36 flagged Pally in Desolace got me to thinking. What a terrible waste of my time to log onto my 60 Warrior, bring him all the way to Desolace, just to make her turn that damn flag off. Or, how long will she choose to remain flagged once I show up? How soon after I show up would she unflag? Five minutes?
I suspect it's an anti-social thing.
Or a trap. Flag yourself. Cry "Heal me!" in Goldshire. Some noob gets flagged healing you. And your buddy, on his Horde Faction Rogue, goes to town on the noob.
What on earth, or Azeroth, are you thinking flagging yourself for PvP in Desolace? Or Elwynn. What is the point??!