I've been leveling my DK for a while now and have run into the question of "Is Mark of blood useful and/or nessesary for ether leveling or raiding?". My knee-jerk response is yes if for no other reason than to help healers in instances and or raids.
With that being said, am I right? or should I just put it away and leave it by the wayside to be buffed and specced into later?