I have two 3D printers. They are very handy, and let me one off parts that don't need to be made of metal in the machine shop. However, are they going to be game changers for manufacturing? Probably not. 3D printing is likely to remain a toolroom method.
In manufacturing, there's a differention between toolroom methods and production methods. If you're only making a handful of something, you'll likely use toolroom methods. It's slower, using more universal tools and keeping custom tooling costs to a minimum. The fixed costs are low, but the unit cost is high. If you're making a lot of something, it makes sense to invest in custom tooling up front to make the unit cost cheaper, with higher fixed costs up front.
Lets say I'm making a custom sheetmetal part. I could do that the toolroom way, with tin snips, drills, files, an english wheel, crimpers, a brake, etc. Tooling costs are low, but I've got a lot of time in the part.
If I'm making a bunch of them, it makes sense to spend the time and money on making stamping/punching dies for a press. High initial cost, but now a low skill operator can tend the machine and knock out parts quickly.
If I'm making plastic parts, 3D printing falls in the toolroom category. Low inital cost, but it's very slow and somewhat finiky. If I'm making a whole lot of plastic parts, it becomes cheaper to invest in tooling up front, and use a process like injection molding, vacuum forming, etc.
