I use it for setting up and testing games before adding them to the main list on my front-end.
It allows you to make changes through a decent user interface, but still use the regular mame.exe
That way if I have an issue, I know the issue is in the genuine version of MAME and not because it's a derivative.
It's been most useful for tweaking video settings for individual games to try to eek a little more speed out of them (California Speed and SF Rush, specifically).
I'm not sure why it's not more popular.
(IIRC, it does come with mamep.exe, but I've never used it.

)