I only have 3D printer for about a month and people asked me that question multiple times already.. It's the question every early adopter gets. (is it really that "early"?) Back in the old days of feature phones, people were wondering why I got Symbian phone that was quite a bit more expensive than regular Nokia brick. That was years before iPhones were a thing, so the answer wasn't as obvious to non-techie people out there as it might be today. (and remember, when it was released, even iPhone wasn't all that smart, no app store, no multitasking, no Bluetooth even) Back then the simple (and real) answer was:
"Because it's cool!"
And that's really the reason why I got my 3D printer. However I feel like the real answer is different. I no longer feel that the 3D printers are cool for the same reason the pseudo-smart mobile phones with proprietary OS were cool. And to explain that feeling, I have to go few years back.
This is where I belong
I've started using Linux in the late 90s. I had no reason really, just being curious about stuff.. I didn't really expect that, but I was instantly pulled in and since then I've never looked back.
In the early days Linux wasn't easy - definitely not as easy as it is now, but there was something different, almost magical about it. The free culture. Sure getting my video or sound card working properly was hard, you had to learn deep system internals to do that. But you know what? You could learn that. And not only that - you could also tinker with that stuff. Suddenly - even with my limited knowledge and no Internet connection to help - I saw the wall falling. I was no longer limited by what the Operating System could do. I wasn't limited by some company telling me what the program does and what it can't do. I could add and change stuff and break it and make it better. My skills were suddenly the limit and it was up to me to improve those.
Linux, GNU and Open source changed the way I look at computers.
The way I look at the world
I own my printer only couple weeks really. And it's a cheap one. (review incoming) But I can tell you already, I started to look at the world differently. Somewhat in a "if all you have is a hammer, everything looks like a nail" fashion, but there's a difference. Suddenly I've realized, that there's a whole set of problems I had, that weren't easy to solve with limited (common household) tools and my (quite) limited skills.
Basic things like broken radiator valve handle had only one real solution - to buy a new one. There has to be somebody making those, you're only limited to selection they offer, often you have to buy them in packs because they won't sell you just one. And if you don't like the design, or you want to improve on it, there's really no way to do that.
As Thomas Thwaites found out while working on his book The Toaster Project, it's surprisingly hard to create simple things that we take for granted. And while you can do some things on your own, especially if you're skilled in woodworking or similar, the most common material that you see everywhere these days is surprisingly out of reach. In fact Thomas even had to cheat a bit and "mine" plastics for his toaster and even with that shortcut, his toaster plastic body didn't look that great.
Sure, 3D printer is cool, but it's definitely not the easiest thing to master. Regular printers don't have the best reputation either, but 3D printers take these issues to whole new dimension. (pardon the pun) So how is it any better than learning some other skills - like the mentioned woodworking for example? Well, there are some major benefits.
One is the selection of materials - you can choose between many common plastics like PLA, ABS, Nylon and their variants, there are flexible options as well. If you rely on 3rd party services for printing, you can also use metals like brass, steel or even gold.
The other benefit is - and this is a big one - that I can share my creation with other people in a way that enables them to take my work and create their own "copy" of it. You can now literary download a car. And while you could share CAD files and plans before, actual creation of the final object wasn't as easy to copy as it is with 3D printer. Especially if you're trying to achieve sub-milimeter accuracy of the copy.
Finally - and this is the biggest game changer in my opinion. Not only they can copy my work, they can improve on it and share the improvements back.
Yet again I saw the wall falling. I am no longer limited by what the manufacturer is willing to sell me. I'm not limited by some company telling me how the thing I want should look or work. I can now design my own stuff, change it and break it and make it better. My skills are suddenly the limit and it is up to me to improve those.
3D printing changed the way I look at world.
So why would you want a 3D printer?
There are services out there, that will print things that you design, so if you really want to just design things and have them printed without a hassle, you don't really need a printer. The notion that you can design something and eventually hold it in your hand as a real physical object was enough for me to change my view of the world.
CAD/3D design software alone could take me only so far. I spent countless hours playing with Blender and I could render the objects to make them look almost real. I've never had decent artistic skills, my 3D renders were very lame, so I ended up feeling out of place with those tools. Looking back, I feel like that's what was pulling me back to 3D graphics and design - that desire to create real object from scratch, starting just with an idea.
And sure, maintaining a printer is pain, printing is not super easy and it fails every now and then, but it makes me better at designing stuff. It helps me learn the nuances of 3D printing and it teaches me to design objects that are easier to manufacture.
So why do I want a 3D printer? Well, because it's cool, but more importantly it makes me a better designer. And remember, my design skills are now the limit, so it's worth improving those.