In "The Answer" Sapphire is escorted by three Rubies to visit Blue Diamond. While she was there, she fused with one of them and caused a chain of events that were very important to the Crystal Gem history.
But, why didn't Sapphire just use a Diamond communicator to talk to Blue Diamond from Homeworld..?
I mean, they had to of existed then, right? I mean, Sapphire and the three Rubies traveled to another galaxy on who knows what, Blue Diamond's throne thingy can float, and the entire arena could float.
I am pretty sure they had Diamond FaceTime back then.
Would've saved a lot of trouble.