While the Pi can run some emulators it shouldn't be used as a key point for the devices. Most of the emulators the Pi runs are 10-15 years old. Emulation has advanced a lot in those years, especially emulation of the classics. Emulators like Higan (SNES) have high CPU requirements (i5-i7 for everything at full speed) for good reason, and the only MAME version I could find for the Pi last time I looked was based on a 0.36 series release, which to give you a timeframe is from when Windows 95 was at the peak of popularity, it didn't run many games and the ones it ran, it ran badly with worse graphics, colors, and sound compared to the versions you can run on even a mid-range PC today. Don't get me wrong, these are cool devices, and an essential part of keeping computing alive, teaching youngsters how computers actually work etc. but if you're investing time into them and expecting a truly authentic emulation experience you're wasting your time.