Id like to think about the fear based tracking system as a technological problem rather thenthan a benefit. As it has been mentioned earlier, the creatures were designed to only hunt humans. They did not want the creatures to be able to go rougerogue and turn on thier createrscreators, hence the first waves lack of breading organs and the use of a one track sesorysensory-identaficationidentification system. However they could just as easily have used base human scent as a means for tracking. It is likely that human fear pheramonepheromone was the only scent the aliens were able to pick out. They may have even picked the scent thinking that it was human aroma, and did not realize that thier sample was tainted.
This explains the some-whatsomewhat random redesigns of the ursa body plan. peoplePeople kept on winning against the ursa dodue to ghosting, yet the aliens never got feed back on the creatures performance, so they simply kept upgrading the creatures hardware. Very similar to cracking Inigma durring war Two only with BO.
More than anything though this is a narativenarrative exploit more thenthan anything, to let the hero win by litteraly overcoming his fear, and to justify its creepy no eyes face. RealyReally a person just needneeds to close in thiertheir scent by wearing a body suite, or sitting inside an air conditiond tank to ghost an ursa. See also the anime Blue Gender and the movie Mimic for variations on this theme. Also the movies Nausica and of course, Pacific Rim on the technological perspective.