3D printing is moderately useful. It will become much more useful when it can produce more than structural parts.
Automatically placing and connecting electrical components is still a ways off, although lots of people are working on it. Until then, CarryTheWhat has demonstrated an impressive DIY method of producing circuit boards on a 3D printer.
The key to how this approach works is a series of pegs connected by conductive thread. By strategically wrapping the conductive thread onto a peg board generated in OpenSCAD, the components of the circuit can all work together.
It’s a bit bulky and crude, but it works. For example, here is a flashlight…