Here's a story:
A staff member's mother had broke the knob off her air conditioner. They tried gluing the knob back together to no avail so she would just have to use pliers to turn the piece of metal left that attached the knob right? Wrong! We can just design something in tinkercad to fix the error.
All I needed was the broken knob in question which I measured out in mm and replicated in the design software using the round roof and cylinder shape. My main concern was that the hole would fit securely so I made sure to measure the height and width of the hole as accurately as I could. I love that the metric system is in 10s. 10cm=1mm where cm is conveniently on most rulers opposite side of the inches. It fit like a glove! I recommend using the strong setting in the cube software so the piece is strong enough to turn.
Imagine a few years into the future when these printers become more affordable. You break a part of an appliance like your expensive vacuum. You email the company with a picture of the part in question and they send you a 3D printer replacement file. You print it out on your home printer (or design the part yourself) and you have found a cheaper (and more environmentally friendly) way to make those appliances last. Besides 3D printing organs, what is more practical than that?