Sensing Nen

When one has developed use of their nen, they become sensitive to the presence of other beings by their deployment of nen. Since every living being creates nen subconsciously, it is a useful skill for those tracking or hunting (both animate and inanimate things). It is also useful in combat, because one can judge the location and relative strength of opponents by the output of their nen. To counter this, techniques that minimize nen output like Zetsu or In are used.