In a way that's my point - it's probably a 5 hour job to print a replacement plastic peg for some toy. 5 hours is $100 for anyone who can afford a 3D printer. Plus the printer's cost. Financially it makes no sense. As a hobby... brilliant and probably hugely rewarding, but the 3D printing lobby would have you believe we'll all have one and nothing will be landfilled any more.
It might take 5 hrs to print it, but do you stand there and watch it the whole time? Plus there are several items I've printed that I could have obtained in no other way.
So 3D printers are great for me, and now I'm on the verge of it being viable to buy rather than outsourcing the printing.
It doesn't make sense to fold in the owner's time when the machine is printing on its own. The real cross over point is when it takes less time to find the part online (not trivial) and get the printer started than it does to drive to the store and find it (if it exists). Then, the cost of the owner's time cancels out.
If you live outside a major urban zone, this driving and finding time can be substantial.
As the father of two young boys, I could make a full-time job of printing replacement plastic pieces for broken toys.