If you legally own the original arcade PCBs, you are generally protected to possess a digital backup. For the rest of the community, the set is distributed via "PleasureDomes" (archival torrents) and private trackers focused on data preservation.
About 50% of the ROMs (roughly 11 GB) in this set represent games that are technically "non-working" in the emulator due to incomplete emulation. Primary Compatibility: Mame 0.134u4 Romset
If you are trying to play arcade games: