Tactics is one of the best secondary skills in the game. At expert level, it allows a hero's army to advance 7 hexes, which is almost half of the battlefield's total length of 15. This also allows hero to arrange his troops most in suitable way for his army's capabilities. Furthermore, hero may take full advantage of the obstacles on the battlefield as a tactical element. Also a valid action is to "turtle" the troops, meaning that arrange the melee units to protect the ranged units. Combining Tactics with speed increasing spells like (mass) Haste or (mass) Prayer, allows even the slowest army to reach enemy lines on the first round of combat.
The downside of the skill is, that same level Tactics cancel each other out. When heroes with the same level in the skill confront each other, neither of them may benefit from the skill, and therefore have one secondary skill less to utilise during the combat.