Well, I think a great advantage in regards to this jutsu is the element of surprise. If the user conceals himself, (Smoke bomb,dust cloud,flash bomb,etc) then casts the justu within the haze/fog/mist/etc. The opponent will have no way of seeing the jutsu being performed (Obviously I am not including sensors,and doujutsu users here.) Therefore they will have almost no way of predicting the arrival of the leeches. But it then also allows for simultaneous attacks due to the fact the leeches still need to travel a distance underground to reach the opponent. So the user can use this very short window of time to distract or what I like to call compound attack the opponent to result in a more accurate attack and get the desired result from the jutsu.