The main advantage to NES emulation is that it's a very mature area of study. High-quality documentation is much more readily available than for other systems, and there's more public discussion of the specific problems that NES emulator authors encounter (both primarily on nesdev.com [1] [2]). There's even a sort of tool-assisted speedrun of writing an accurate NES emulator, if you're into that sort of thing [3] [4].

[1] https://wiki.nesdev.com

[2] https://forums.nesdev.com/viewforum.php?f=3

[3] https://www.youtube.com/watch?v=y71lli8MS8s

[4] https://www.youtube.com/watch?v=XZWw745wPXY