The reason we love 3D printing so much is how much it doesn't cost. The traditional methods for creating prototypes are time consuming, expensive and not always easily reproduced. Even something simple like a plastic frag disc can cost thousands of dollars in design and tooling costs to produce just one. Now multiply that over a few dozen design changes and it's enough to make anyone cringe. But with 3D printing, a new prototype costs just a few dollars and we can have it in less than 2 weeks. Now for those thinking 2 weeks is a long time, it's because we don't print in-house for most of our things. Our little FDM printer can't quite get detailed enough for the tiny little parts we are making, so we outsource to the big guys with the crazy fancy printers and they send us back very detailed, highly functional pieces.
However useful 3D printing is for prototypes, it still lags behind when talking about commercial production. 3D printed prototypes can be made in days instead of months and cost a few dollars instead of thousands, but with mass production, the traditional injection molds win. Injection molds can create new parts in just a few seconds and if using a high quality mold, those parts can be even more detailed, consistent and affordable, which is very important because lets face it, no one is going to spend $7 and wait for 2 weeks just for one frag plug, no matter how awesome it is.