Split sets are the standard for most emulation builds. The "parent" game contains the bulk of the data. The "clone" files only contain the specific modified chips (like text translation or alternative music).
Excellent for cross-platform play (Android, Steam Deck, Raspberry Pi), though it uses a slightly different ROM compatibility list than standalone MAME. A Note on Legalities and Safety Mame Full Set Roms
There are several ways to obtain Mame Full Set Roms: Split sets are the standard for most emulation builds