If u got a DK on wow and u want to make a glitch or something like that and u got dual spec u can make yourself having as much life u have in frost presence in unholy presence. If u want to do that u shall press on frost presence so u are using it switch to other talents so change presence there and swap back to your talents u had and voila u got much life in blood/unholy presence.
a tip if u are DPS and specced in improved blod presence is to do the same i told you but change to unholy and i think u get much life and more movement and buff from improved blood presence!!!