The benefits of using cast iron for spears lie in its inherent properties. Cast iron, known for its excellent castability, is resilient and suitable for manufacturing sharp, sturdy spearheads that can withstand the rigors of battle. The material's high carbon content contributes to its hardness, allowing for effective penetration without easily blunting. Moreover, the casting process enables the creation of complex shapes that traditional methods cannot replicate, leading to innovative spear designs tailored for specific combat contexts.