Arcade ROMs are intellectual property. It is generally only legal to own them if you possess the original arcade PCB.
: The full set is significantly smaller than modern "Full Non-Merged" sets, which can exceed 100GB. mame 072 roms exclusive
A full "Merged" set of MAME 0.72 ROMs (excluding CHDs) is roughly . A full modern MAME 0.260 set (excluding CHDs) is over 70 GB . If you are building a Raspberry Pi 3 or a retro handheld with limited storage, the mame 072 roms exclusive pack is the only logical choice. Arcade ROMs are intellectual property
Many "all-in-one" retro handhelds come pre-loaded with 0.72-compatible sets because they offer the best balance of speed and game variety. Understanding ROM Set Differences mame 072 roms exclusive