hmm... i don't see the point to that one, just confuses matters. Good thing j5 now checks for both for backwards compatability reasons.
I think that's why mame has both, now. I think the '-_directory' is supposed to indicate that it only takes one folder and '-path' means it can take multiple folders; IIRC ctrlr used to only be able to have one folder. Whether mame keeps both is another issue.
Options with both path & _directory (what shows in mame.ini on left, alternative in parentheses):
artpath (artwork_directory)
ctrlrpath (ctrlr_directory)
Options with only path:
rompath (rp)
samplepath (sp)
inipath
Options with only _directory:
cfg_directory
nvram_directory
memcard_directory
input_directory
hiscore_directory
state_directory
snapshot_directory
diff_directory
comment_directory
And just for fun, the only option with four ways to do the same thing:
resolution0 (resolution) (r0) (r)