Development of specifications with cross-functional teams

Why should the development of specifications be done with cross-functional teams and what is the benefit to the organization?

Specifications are design, performance, or test requirements for a product or item under development. These are good to have with cross-functional teams because once the design and requirements are finished the item is basically finished and just needs to be manufactured. This benefits the organization as it decreases the amount of gray area there is for a product, and makes sure the product will meet the requirements. If there are not specifications and a product is bad, it is bad business.