Hi!
When browsing through current playlist's contents, you might want to start listening to a certain song. At the same time, you dont' want to interrupt current song.
So what do you do? You move the song next to currently playing song — so that it will play next.
But that's not very convenient. You have to drag your song all the way through your playlist. Also, you might forget whether currently playing song is above or below your current position in the playlist.
A simple solution could be a "Play next" command in the context menu of a playlist item. This command should move selected song next to currently playing song.