there's multiple ways this data could be used, including:

• improving matching listens to MBIDs
• assisting in playlist creation, showing tracks in your library first in searches
• showing your music library on your ListenBrainz profile

these could possibly be pulled automatically, as there's two collection types for owned music, one for releases, and one for recordings. I think it should also be possible to exclude certain collections, say you've got a collection of audiobooks and audio dramas you don't want showing up in playlists, or a collection of vinyl records you haven't yet ripped