" Bullseye is used in case radio communications are intercepted by the enemy - since the bullseye point is agreed upon prior to the flight and is not stated over the radio, the enemy will not be able to determine where you are referring to if you use bullseye terminology. In addition, using bullseye coordinates helps improve situational awarness, since it is an absolute frame of reference. If AWACS tells another aircraft that they have enemy fighters at "3 o'clock, 25 miles", you have no idea where they are. However, saying that the fighters are at "bullseye 120 at 100 miles" tells you exactly where they are located "
THAT being said...once the fur ball starts I want to know where the bad guy is in relation to ME...NOT some imaginary point on the ground...at that point we all know where each other are.