Since the dog days of the early 1900's, when Henry Ford was ram-rodding the idea of an "assembly line", while his customers were asking him for "faster horses", OEM's (Original equipment manufacturers) have sought out Machine Shops as their primary source for castings. It made sense, the machine shop was the last stop in the line, so from a material flow standpoint, the OEM buys from the machine shop, and the machine shop sources the castings to a foundry.
Product design tailored to the CNC machining process is one of the easiest ways to lower production costs, yet it is often treated as a cursory consideration during the design process — not the major cost (and time) saving factor that it can be. To be clear, in the early stages of design, unfettered brainstorming and concepting is fine (and even preferable). Though as you fine-tune the product and approach the stage of generating technical drawings to be used for production, it can be extraordinarily helpful to begin incorporating best practices and standards for the CNC machining process.