I think that 3D printers will revolutioize workshops the way Guttenberg's movable type revolutionized printed communication.
So YES, if you have the inclination to learn about them, do so.
But I would advise against learning about them from a repairman's (service technician's) point-of-view. Instead, learn about how to CREATE with them using 3D CAD and (if this applies) Numerical Control methods. Then you would be able to create you own visions AND, if you wished, work as a consultant or "short job run" specialist to other businesses in your area.
3D printshops will be the new incarnations of the old "village smithy" shop.
Carpe Diem!
As for what they are:
Visualize your desktop inkjet printer: that is a 2D printer. It prints on an X and Y axis.
The 3D printer is very similar to your inkjet printer, except that instead if squirting droplets of liquid ink onto a sheet of paper, it squirts droplets of molten plastic (usually) onto the work surface. The molten plastic rapidly cools and the printer then advances on the Z axis and repeats the process. In this way the plastic is deposited as "slices" of the thing being replicated.
There is a site for a company called SHAPEWAYS that allows people to market things they have designed. The site is here:
Most of the items offered are less than 4 inches square, and they do tend to be pricey, but this IS new tech, and the print engines (the machines) and the printer "ink" are expensive.
Bathsheba Grossman was one early adopter of 3D printing technology. She is an artist who has a better-than-average grasp of mathematics, and she produces sculptures like "Metatron," shown here:
This is a great example of what you can do with 3D printing.