3d printers are good for prototyping (mostly you print the molds for your tools and cast the real tool off of that) and modeling for architecture presentations (like i often do).
there are printers that use plastic and some are starch that you bind with resin. the new ones that a science channel show featured could print tools that you can actually use right from the printer which I assume is not going to be consumer friendly in terms of price anytime soon because they were designing it for use in space.
if I can afford a good sized 3d printer (maybe 8x8 at least) I would get one. also check out laser cutters. you can build so many cool stuff with these tools.
