Or it won’t happen when you’re watching, because then they’re thinking about what they’re doing and they don’t make the same unconscious mistake they did that brought up the error message. Then they get mad that “it never happens when you’re around. Why do you have to see the problem anyway? I described it to you.”
In addition to “format shifting,” which is a well-recognized use case, and game preservation, which is a huge and under-recognized public interest in emulator development, emulators are also used for the development of homebrew software. E.g., there’s a port of Moonlight for the Switch, which lets you play Steam games streamed from a PC using your Switch, letting it serve many of the purposes of a Steam Deck. That’s huge! It would be way less practical to develop this kind of software if you could only test on real hardware. Testing on real hardware is also essential, of course, but testing on an emulator is vastly faster for rapid iteration.