Armorer skill is unquestionably one of the most useful secondary skills in the game. As it reduces all physical damage at expert level by 15%, it effectively increases allied creatures' health by 18% (17.64% to be excact). This is not strictly speaking true, as the damage calculation is somewhat more complicated, but it gives a good approximation of the benefits of armorer skill. Reduced damage leads to fewer casualties in battles, and more troops for the next battle. Especially in extra large maps this may give the needed edge to vanquish the enemy.