reasons from the top of my head...
- because it allows easily to know which are the Jpn originals corresponding to some US/Eur games, and viceversa - because some roms are shared, for systems where we have been able to document proper multichip PCBs (like many NES and SNES games) and for systems with multi-disk releases where only a single disk have been modified across revisions - because anyway MAME shares most of the loading code across arcade and home system roms, so that the support is already there and it makes sense to exploit it ![](//www.mameworld.info/ubbthreads/images/graemlins/wink.gif)
If more come to mind, I'll reply again
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