Why doesn’t anyone bite the Shadow Priests first?
While I don’t quite go to the length of Keredria and their raid’s Musical ICC but everytime I get to Queen and the biting assignments are worked out. I get the Oh Oh Oh Sexy Vampire song in my head
Sexy vampire,
I’m falling in love
So just bite me baby
And drink all my blood
BITE ME ! Mainly cause getting bitten 1st = sexy dps. Just think of all the extra VE healing you would get to the party = Less stress for healers is a good thing
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Pugnacious Priest's Warcraft Blog 
Yea, right, like anyone thinks of the healers. If there was a fire that gave a 1% damage buff but did 50% health per second, people would stand in it. Well, they’d stand in it even without the damage buff, but they wouldn’t be trying to do so.
Hodir – people standing still collecting stacks of the debuff needing healing while increasing their Dps is a perfect example
We do bite the Shadow Priests first. I get dibs because I’m specced for 2/2 VE and the other full time Shadow Priest is my first bite target.
Maybe your guild is just set in their ways – perhaps they’re not used to the awesomeness of Vampiric Embrace!
When fighting the enrage, biting Shadow Priests first seems unlikely to be your best move, simply because the movement on that fight can leave Shadow Priests as a disadvantage for MaxDeeps. However, once you’re no longer bumping enrage, having a Shadow Priest putting out twice as much healing is definitely a win, no question about it. Most people just don’t think about it.
Well it’s also possible the healers don’t need help. Of course there are a lot of circumstances as well, if your guild is struggling to beat the enrage timer, it doesn’t make sense to bite a shadow priest first.