The Backdoors serve as way to break up the monotony and tension of Transistor's major plot. After you get past Sybil, you can start to experiment. They serve as something between minigames and tutorial missions, challenging you to clear optional rooms of generated foes in several specific modes — clearing everything within a certain time limit, within a single planning Turn(), outlasting waves of enemies, only using a specified set of functions. It's a challenge at your pace, and in return you unlock an ever-expanded soundtrack to bask in.
And basking really is the name of the game. While you can bop around a beach ball to your heart's content (which is pretty fun all told), one of the real rewards is unlocking the hammock. You can watch the sun fade away in the beautiful horizon and listen to the tracks you've unlocked throughout the game. Supergiant games at this point are known for their scores, and this game is a big contributor to that reputation. It's a nice opportunity and excuse within the game to chill for a slow moment, watch the stars twinkle out, and listen to Red sing.
Because Red's voice — her career as a musical artist, the songs that make her famous, the gift of expression that made her a target — is a pivotal part of the missing-piece jigsaw puzzle of the game of Transistor. Not just the story, but the game, which starts as she's lost it and is haunted by it throughout. You can hum at the push of a button, which is novel and reflective and feels charming your first time through. But it's as much a sign of what's lost as the Transistor speaking to you is.
But in the Backdoors, in this little hideaway or never-been, this destiny islands pause button breakaway from the fight-for-your-life, we can put a record on the record player. The recordings of Red's music persist after her voice is gone, and we can experience ourselves, or through her eyes, recontextualizing the meaning of the song through the present moment (and present company).
When we leave the backdoors, Sybil, now in the Transistor, will be a big Help(), leading us to her former collaborators in the Camerata. We may not be able to get away with this. But for now, we can take a moment away from this, take a moment to breathe by the beach.