Originally Posted by
Malm
The thing about obliterate is that when you use it, it consumes all the diseases you got on the target (you can talent this so there is a 90% chance it won't consume the diseases, 'annhilation, tier 3 in the frost tree'). So obliterate is more a finisher than a general dps skill. You want to keep as many diseases up at all time since you'll do more damage that way. Point is, Blood Strike is your main dps skill, whereas Obliterate is more a finisher when you don't care if the diseases is on the mob after the strike.
Personally, I solely use Blood Strike, I touch Obliterate once a day while playing if at all.