I'm sorting my music in playlists like by decade or occasion and genre or mood. E.g: "Summer House", "Summer Hits 00s", "Summer Hits 60s/70s" and so on. Or like a playlist for all 90s Hits I know, one for 90s Party Hits Best Of and one for 90s Party Hits (including songs I don't like - but may be asked for sometime) and 90s Hits (that you wouldn't play on parties) split by different categories...
Splitting the music into different subgropus by date or occasion/mood leads to many duplicates and a enormous amounf of playlists and playlists which combine the content of others. By the time, it's getting a little messy and I'm not quite sure whether using subfolders would rather worsen orientation.
Maybe some kind of linking or grouping possibility without changing the original playlists could help out, like when I group my wireless speakers when I want to listen to the same music in multiple rooms. The Play Next Function is not really what I'm looking for.
A similar idea has been posted here: https://community.spotify.com/t5/Live-Ideas/Playlists-Play-multiple-selected-Playlists/idi-p/1240798
Please add your comments/votes there, and reach out if you need any other help 🙂