Imagine manufacturing something as simple as a cylinder.
- as stl file the machine would have to mill individual tiny planar facetes.
- as true cylindrical geometry (extruded cylinder) the lathe simply turns the stock as the tool moves linearly.
I recommend you sign up for a basic machining class if you want to continue in this field.
I worked out on the shop floor for 8 yrs as a machinist and it always bothered me when designers would design some feature that couldn't be manufactured or manufactured at a reasonable cost or that a customer wouldn't look at and consider garbage.