Generative Design offers the exploration of multiple alternatives according to the parameters you want to control from a design perspective. Such as weight to structural loads, materials, spatial restrictions, manufacturing methods and cost constraints. All these parameters are iterated by a software that provides you multiple outcomes. There's not only one solution to your problem Generative Design allows you to explore multiple solutions.
Along with Additive Manufacturing Generative Design are meant to work together as both technologies complements each other. One brings the design solution and the other brings the manufacture solution.