Why is tamahagane folded?

Could you elaborate on the purpose behind folding tamahagane, the traditional Japanese steel? What specific advantages does this process confer upon the steel, and how does it contribute to the overall quality and characteristics of the final product, such as swords? Is it a technique rooted in historical tradition, or is there a scientific rationale behind it as well? I'm curious to understand the significance of this step in the steelmaking process.