Template:Attribute-stub Strength is the Warrior primary attribute. It gives 1% armor penetration per attribute level when using attack skills. It also has the secondary benefit of enhancing strength-based skills, which mostly relate to doing damage or surviving.
Strength is a requirement for some shields. There are also shields that require Tactics.
Secondary Warriors do not have access to Strength.
Even if a Warrior does not utilize any Strength skills, it's recommended that any spare points be placed into Strength, if only for the purpose of dealing a little more damage when using attack skills.