I guess the Approved section isn't actually unused. The Approved section is for beatmaps that are marathon maps or things in the beatmap that is wrong but the BATs (or QATs) consider OK.
Approved (according to the osu!wiki):
Following up from #ranked, a BN can approve these beatmaps if they are longer than 5 minutes long (aka marathon beatmaps) and/or that don't follow the ranking criteria but are considered "okay" by a BN.
Note: Beatmaps (that are less than 5 minutes) are planned to be #ranked, not approved!
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