The problem with 'doing things that you can only do on a 3D printer' is that you have locked yourself into a 3D printer.
My plan as a hardware entrepreneur would be to 3D print prototypes and MVPs, maybe even the first production run. Then transition to prototype molds or CNC machining with a lot of setup/teardown. Finally you go with full blown steel molds, dedicated machines, fixtures, etc.
If you design for for only 3D printing, you can't scale past 3D printing.
But that can be said for any basis of any tool or technology. Your use of CNC matching creates a dependency on that tool, and it's advantages and disadvantages. You've locked yourself into that tool if you don't want to change the way you work. A shift to any other tool will come with modifications to your work, and I don't think that is unique to 3D printers.