Revelations communicated by psychic or mystical powers are usually only revealed to one character at a time, so it's a sensible occasion to use note-passing to convey what knowledge is gained. Even if the PC immediately shares the information with the other characters, it becomes filtered through how they interpret the note from the GM, rather than having everyone hear the same words direct from the GM's mouth. This one step of removal can create a very different message for the characters who don't see the note, as it's easy for details to be left out, embellished, or interpreted in ways that would not otherwise happen. So notes can add more flavour to a game than just mere secrecy.
Yoda: Open your mind to Vader, you must not.
GM: Corey, make a roll. If you want to.
Obi-Wan: Fool of a Luke!
GM: Here, take this note.
Luke: Whoa... He's...? Oh my god!
Obi-Wan: Look at me! What did you see?
Luke: I have to go!
Obi-Wan: You must stay with us and finish your training.
Luke: You're not coming with me?
Obi-Wan: This is the Jedi homeworld.
Luke: Right. Because there's one Jedi left, and Yoda's here.
Yoda: No! Thousands there are. The midi-chlorians of the transcended Jedi I brought here.
Yoda: In Lord Elric Fluffypants they live.
Obi-Wan: We residents prefer "the tree".