In AM, a part is generally visualized as a set of horizontal layers. AM requires either having layers and a method to join them or a method to make and join them. To have layers means to bring them from somewhere if that is required. In almost all AM techniques, making a layer is accompanied by its automatic joining with an underlying layer (or a platform), implying that making a layer means both making and joining. AM simplifies fabrication by reducing the fabrication to making layers and joining them. It is called simple on the assumption that making layers and joining them are simpler than making the whole part at once. If this is not the case, it is not simple. For example, if a cube is made from a bigger cube by machining, it is simple. If AM is used to make this cube layer by layer, AM does not simplify the fabrication but makes it complex. Because a number of layers need to be arranged and joined, while machining requires only trimming a bigger cube. Thus, only when a part is complex, AM can be invoked to simplify the fabrication.