"Save song" new feature

I tried hard but I haven’t figured out…
What does the “save song” feature mean?
It is available to “save song” when selecting the songs from a playlist.
Is it possible to pre-buffer/download the tracks as it can be done at Spotify app?

You can save songs in the spotify playlists in the spotify software (APP) but not in the DJay software, unlike with PulseLocker and Serato.

On the DJay Pro has a feature called “Save song”. But I dont know what that means.