When you load someone’s song into the composer and make an edit, the song is saved locally, and you can publish a remix through the plus button.
It will also leave a “trail”, so when you remix a song, there is going to be a link added automatically to the description that point back to the remixed song.
So, for another community song for example, you’ll be able to pass around the song by remixing the file from the previous person and on the final “remix” you’ll be able to click on that link to back to the previous “remix”, which will have itself the link to the previous “remix” and so on until it goes back to the first file.
Could also be used as a way to easily collab with someone by back-and-forth remixing of unlisted versions of the song, then release the final version as listed.