The "Clone" game relies on the "Parent" zip to run (standard for most reference sets).
These files are massive. While a ROM might be 2MB, a CHD can be several hundred MBs or even GBs. mame 2014 reference set mame 0159 roms chds top
It is the specific version used by the mame2014_libretro core. The "Clone" game relies on the "Parent" zip