Sorry, badly explained.
If you are in a playlist you can add songs to that playlist, that’s great.
it would also be really cool to be able to pick a song and send it to multiple playlists.
Example: Let’s say I’ve just bought the Maggie May backing track, sorted the lyrics and other metadata tags and now I would like to send It to my 70’s playlist and my Rock Playlist. Much easier from that starting point to be able to send it to the playlists rather than going the long way round opening up the playlists and adding the song. If you are doing say 20 or even 50 songs that would save a lot of time and keystrokes.