Depends on what your goal is. If you are trying to reduce the list to a more manageable size, you can use the filters like Adultery suggested. In my case, this reduced my romset from ~7000 to ~2000. There's stuff in there I would never play, but I leave it in there in case someone else might want to play it. BUT, I don't have duplication (US, JAP, RevB, etc) for each game in MAME. If on the other hand you are trying to reduce the size of your romset's footprint on your hard drive, that's more difficult. If that's your goal, I'll wait to hear it before I start thinking about how to deal with it (non-manually).