3D printing has the power to change the world, and in fact - it has been doing so for the past 20 years. When it comes down to getting certain parts custom manufactured, 3D printing is usually there to pick up the slack.
Some people enjoy designing characters and various parts on the computer in their spare time, and don't have thousands to spend in seeing their creations come to life. These artists are using 3D printing to create full color prints of these characters for their personal use. If you've ever seen a talented 3D artist go to work on a part, product, or character, you'll know that it takes time. Of course every model is different, but these designs can truly be pieces of art. To bring a project that took over 20 hours of skilled labor into the physical world is impressive. 3D printing is here to bridge the gap for these artists that can't afford to send out an order overseas. Some full colored models can be made for under thirty dollars. Of course you can spend as much as you'd like on certain parts, but 3D printing is available for a pretty inexpensive rate at some places if you are an artist looking to create something.
Perhaps you don't really have a desire to produce parts "just to do it", but you want to actually make a functional part. Maybe you're interested in eventually mass producing a part, but you need to prototype. 3D printing is definitely there to pick up the slack in this instance as well. 3D printing has a large variety of materials to choose from when actually producing parts. Some are better than others for certain models and designs, but there is a material for practically everything. If you need a metal that can withstand the heat inside of a jet engine, you can use 3D printing. If you need a product that can be flexible or rubber like, this technology is for you. If you need a full color model, it is for you. If you need a part that offers chemical and heat resistance, this technology is for you. I'm not going to say that 3D printing is going to be there for absolutely everything, but at the same time I can't think of anything right now that couldn't be prototyped through this technology. 3D printing can be pretty expensive in some cases, and not all machines can produce large pieces, but aside from that - there aren't very many downsides to this technology.
Within the past few years, this technology has been blowing up at an exponential rate. There are 3D printers being placed by hobbyists to have in their own homes. There are quite a few international companies that offer this technology as a service. There are tons of local facilities across the world doing it as well. Within the next 10 years, this technology is going to be significantly changing the way that we look at manufacturing goods and parts.