In WOW it is not so fun, first you have to have a few other people to assist you and then the DG 'marks' a person to be sacrificed and interstingly enough YOU can be the one sacrificed. Yeah, that's right, YOU, the summoner, the one who brought the beast into the world!
Despite the DG's bloodlust it can make a powerful ally if you are a decent Warlok of course, cause you would [okay, should] have been enough to summon the thing AND force the thing to submit to your will, evil or not. DG's usually don't follow any mortals plan willingly and only go by force so you must 'tame' them but this doesn't last long.