An amazing thing about 3D printing that should be mentioned - the HUGE variety of models already out there for free download.
One day, my car wouldn't start. I suspected the clutch interlock safety switch had broken off again. It's just a little rubber bumper that fits on the clutch to triggers a switch when you depress the pedal. Without the little bumper, the car doesn't know you have the clutch depressed, and you're stuck.
This time, I had a brainwave - I'll go back to the 3D printer in my office and design a replacement! I was about to start measuring and modeling, but then I thought if my switch had broken twice, it must happen to other people too. A quick search brought up a design for the exact part for my exact model and year - https://www.thingiverse.com/thing:2447785. Ten minutes later I was on my way home!
The moral of the story is you often don't even have to design the model yourself. Although that's usually the fun part - I admit I couldn't resist tweaking and re-printing the clutch switch later, the original one made a tiny clicking sound when I pressed the clutch... 😡