Personal classification is key, I guess, because your two examples are
alien to me.
> Music ks a good example. Most people want to organize by album, artist, year, genre, or song title.
I assumed this is because that's what software is limited to, and people cope, and the only people who really organize like that were the record stores owners. Because personally, this in no way even resembling how I think of my music collection, or how I pick what to listen to.
For me it's usually by theme, personal "feels like they belong together" connection, causal relationships (e.g. music from the same trip I went to in high school), or artist but defined loosely, I.e. tolerant of the fact that artists collaborate and perform together.
> I like to order my photos by outing or by subject.
Outing, yes, but by-subject is alien to me. Most of my photos have exactly zero people, or anywhere from 2 to 20+. Single subject photos are oddity, and I rarely feel the need to organize by them. Events, then by date, then maybe by location.
In both cases search turns out to be the answer, but with photos it's phenomenally unreliable due to vendor fucking with or stripping metadata.