True, if you have a specific start/stop you need. When I worked for Moen, we needed to actually model threads for our plumbing fixtures, so the tool designers could create the spinning cores for the internal threads.
3D printers are nice, I worked at a place that had 2 large SLA machines in-house. The one thing I will say, is that I think people vastly overuse them for prototypes. There are some parts that are made cheaper, faster, and far more functional if machined vs. using a printer. After working there for a coupe years, I came to the conclusion that for simpler parts, machine them, and save the SLA/DFM processes for really complicated surfaces like cosmetic/ergonomic parts (especially with multiple colors/durometers), or castings (especially with internal passages) that would be too difficult to set up for a prototype. And with the 5-axis desktop machines available now that can easily do these surfaces quickly and cheaply in REAL plastic, I'd say that even less parts should really be made on a printer.
Really, a thorough evaluation of the parts is needed. For instance, on the prototypes I'm having made for my new design, I'm having all the parts machined, in stainless, aluminum, and PEEK. At the end, I will have parts I can functionally test undere our real working conditions. In contrast, the design house we used for the earlier design we're replacing, made all their early prototypes in SLA, and as such they're completely non-functional. Just be careful to evaluate your needs before deciding on a method.
