Its most effective on monsters that can drop more than one item. (Cow queen, mappo, othuyeg, ssshaa serpents, stitches, plaguelands monsters, inferno monsters, other bosses) Its less effective in inferno cows since they only drop one item each. So the time spent isnt worth the potential reward. I don't have any hard evidence for this, but I seem more likely to find divine gems from stitches, cow parts from the queen and puzzle boxes and tyrael keys from horking in plaguelands than from normal drops. I havent noticed any special luck in dreamlands though. That being said, it basically gives you 1.5 drop chances per run; (about 50% hork chance) which can turn 100 othuyeg runs for a puzzle box into 67.