So, what do a shadow priest to the table? We got no AoE attacks, most of our attacks is DoTs or channeleds so they can't crit, and our only real crowd control spell be Shackle, what only works on mobs to stupids to realize they's dead. Even then, it don't work on them annoying Fersaken rogues in battlegrounds. /humph And ya, we gots Psychic Scream, but it's usually best we leave fearing to the experts.
One thing what we does have though is Vampiric Touch. This damage over time bugger also restores mana to everbodies in me party, at a rate of 5% of the the damage I does, as long as it be running. Now it lasts only 15 seconds, and takes 1 and a halfs to cast, so it do cut into me time fer throwing higher powered attacks. And it ain't like infinite or nothing. But still, when yer raiding, every little bit helps.
Now, is kinda hard fer me to tell how much difference it makes, since I's always used it. But I did listen in on one of our holy priesties the other night, ta see what that touching action were doing fer her:
"Yes! baby! Fill my mana pool! Just like that, Baby! Don't stop! DONT EVER STOP! YES! YES! YES! YEEEEEEEEES!!!!!!!"
(Is concealing her identity outta privacy respects.)
So, there ya has it. One of the benefits of havings a shadow priest along when ya go offs ta kill big bad bosses.