Nowadays, almost all manufacturing vendors are using CNC controlled machine (lathe, mill, water jet, plasma cutting, and router) to manufacture a part. Do they need 2D drawing for machine a part? That really depends what kind of cut they need.
For 2D cut like water jet and plasma cutting, all they need is DXF file. DXF file contains the shape of a part which all the need for generating G-Code or any other CNC code. So for 2D cut, vendors generally not need machining drawing.
For 2.5D or 3D part. Machinist usually ask for 3D models if the geometry is complex. There are software like Solidworks CAM, NX CAM, and Artcam can generate CNC code directly from a 3D model. If there is no special requirement, CNC machinist can get what they want from 3D model. However, for complex engineering part, threads information, surface finishing, and tight tolerance may call out in 2D drawing. In this case, machinist will check carefully what features are called out in a 2D drawing but not include in the 3D model. So 2D machining drawings are required in this case.
In summary, 2D drawing are not always required for manufacturing. However, it is a good way to make machining drawing for revision control purpose and quality control purpose. In addition, mark up the drawing will be easy if you have a 2D prints while discuss with customers.
