You can create a way for fans to save your song to their library or playlist in advance of the release. Why do this? If Spotify notices that your song gets a ton of saves or playlists on day 1, it will trigger their algorithms and potentially pop your song into various algorithmic playlists like Discover Weekly, Radio, Your Daily Mix, Releaser Radar, Radio, etc. And the more saves a song gets, the more likely a Spotify playlist editor will add it to a playlist.