One of the biggest advantages one can get over another
in a battle, is the advantage of surprise. Many times, surprise
allows one to control the battle. Also, being surprised makes
it easy for one's foe to keep him from leaving the battle.
If one has keen senses and is aware of his surroundings,
he can sometimes avoid ambushes, and walk away unscathed.
Simply using the skill will cause you to turn the skill on/off.