Template:Attribute-stub Strength is a Warrior primary attribute. It gives 1% armor penetration per attribute level when using attack skills. It also has a secondary benefit of enhancing strength based skills.
Strength is requirement for some shields. There are also shields that require tactics.
Secondary Warriors do not have access to Strength.
Strength is a recommended characteristic to level up, as it effects a large variety of things the Warrior does. It can increase the damage your weapon does also.