Most of the time people utilize 3d printing as a tool in their design process. They use prototypes to verify form and fit, check ergonomics, use as production parts, or to catch costly errors before the manufacturing process is implemented. Architects also use 3d printing to show how a project will look when completed.
Casting and Molding are manufacturing processes that have been around for 6000 years. Generally, the process involves pouring a liquid material into a mold, or hollow cavity, of the desired shape and allowing that material to solidify.
Much of the time, 3D printing is utilized for prototype creation not final production. Temporary products are created to test and measure how well a product will work before final design approval and before tooling is set up for the final product.