A 3-D printer has been taken up to the ISS, specially designed to be able to work in zero g, where gravity feeding of the formative material won’t work.
It’s been heralded as a potential new method of providing the station with spare parts without having to wait for delivery by the next available supply launch. However, reliance on this would mean the need to stockpile supplies of difference resources, metals, plastics etc, to cover the various tool, mechanisms, circuit boards etc might be needed. This could be a significant mass that would need to be launched and stored on the ISS and might not in itself be an efficiency saving.
However, there are three (off he top of my head) scenarios where in-situ 3D printing could be a major boon.
Delicate items: a rocket launch will always subject payloads to significant g-force, not to say vibration, and some items might not be able to survive the trip. Being able to build items on the space station would be a solution to this
Large payloads: some items may be too large or oddly shaped to fit within the launchers fairing. Albeit a large printer may need to be built in orbit first, but an ability to build large structures could vastly increase to range of things that could be done in orbit
Where resources are already available: the area that could gain most from 3D printing would likely be where there are already resources available, but delivery of finished articles is difficult. A Martian base could perhaps manufacture its own spare parts, structures and tools from locally available metals, sand, and synthesised plastics. Once this industry is perfected, the need to launch new hab units, return vehicles, greenhouses etc could be made redundant.
Of all new technologies in the pipeline, this could be the most vital for moving from a Martian visiting mission to constructing a permanent base.