I was working on code for a pinball machine for Stern back in 2005. I had a memory corruption issue and Stern's crusty old 6809 hardware didn't have anything resembling a real-time debugger that I could use. There was no time or budget to get a 6809 ICE procured and running.
So I loaded up my code in PinMAME and let it run. I was able to watch memory in real time and caught the bug in an afternoon. It would have taken me a week or so doing it by hand.
So thank you, MAME.