These will replace the simulation / hack that allowed the games to run. The MCU supplies the checksum for the ROMs and allows for the regional "If you are playing this video game outside of the country of Japan.." warning.
While the impact on the MAME user is minimal the arcade collector now has the ability to restore these MCUs should they ever fail.
There are still a dozen or more of these i8751 we need to get decapped and dumped. If you can help please contact TeamEurope through their website / blog.
A couple more steps forward in the never ending quest for better emulation!