Everyone use to smoke, it was something you didn't need equipment for.
If you have no idea behind which wall a pipe terminates or don't know which of 30 pipes runs to [say] the back room you blow some smoke into it (or a lot) One would mostly use it because it is really fast. Non smoking solutions take considerably longer. One might put a pull string in the tube, if you need to wire it anyway that wouldn't take much extra time but ideally you start pushing the spring into the tube on the side closest to the sharp corners. If there are many pipes on that side you would start pushing on the other and might get stuck. If the curves are really smooth the spring could drop out of the tube. You could need an extra set of hands (more expensive). With the smoke test you could push the spring in from the other end.
If there are wires in the tubes you can tie them together and use an ohm meter to find the right tube. You might have to walk up the stairs 10 times.
A local exterminator does smoke tests for the integrity of the plumbing stack: pump smoke in the outside drain, and see whether it all goes out through the roof vents, or some escapes within a house. That's how they found where rats were getting into our basement--a plumber had removed a vent pipe and had not secured the end.
If you have no idea behind which wall a pipe terminates or don't know which of 30 pipes runs to [say] the back room you blow some smoke into it (or a lot) One would mostly use it because it is really fast. Non smoking solutions take considerably longer. One might put a pull string in the tube, if you need to wire it anyway that wouldn't take much extra time but ideally you start pushing the spring into the tube on the side closest to the sharp corners. If there are many pipes on that side you would start pushing on the other and might get stuck. If the curves are really smooth the spring could drop out of the tube. You could need an extra set of hands (more expensive). With the smoke test you could push the spring in from the other end.
If there are wires in the tubes you can tie them together and use an ohm meter to find the right tube. You might have to walk up the stairs 10 times.
Non of it is much like software development.