As per http://wiki.musicbrainz.org/User:Reosarevok/Overview_options

"While we've always shown release groups by default even if they only contained unofficial releases, the problems of that have become more apparent lately. An option would be to only show them by request. Should we do this? If yes, how? Should the options be official/all or official/unofficial? (the latter sounds more useful for people who care about bootlegs, but one of them should tell us!). If a release group only contains releases with no status set, they should probably appear on the default list - that'll make people more likely to fix them if they're actually not official!"

Voting results: Separated Official and Unofficial listings, with RGs with no official releases not being shown by default in the Overview. RGs where all releases have no status set should stay visible so they're seen and the releases cleaned up (keeping them hidden might make more sense in theory but I suspect it would just make people add duplicates).