It will be nice if you could send a notification to your friend to listening to same song that you are listen to, at the same time.
The functionality is to play the track exactly in the same time as you are listening to.
The user gets a notification and decides if want to listen.
It could be work with songs and full playlists.
If you and your friend are huge fans of a band that just release a new album, and you want to listen to the new songs together but you are not at the same place. You can use this feature.
A similar idea has also been suggested here:
Add your kudos and comments there please! ;)