Mass production is great for churning out lots of identical items.
This tech ushers in the age of fast, custom, one-off production. As someone else mentioned, 90% of hearing aids are now being made on 3D printers. That's an example of where mass production is possible, but customization is better, and 3D printers make it feasible.
I'm sure many many more applications like that will appear, in areas where people put up with mass-produced items, but customized items would be better and will now be economically viable.