Haroun consistently equates juggling with storytelling, as he often thinks of his father, Rashid, as juggling many different tales when he tells his famous stories. When Haroun meets Blabbermouth and sees actual juggling, and skilled juggling at that, this relationship is confirmed. Juggling, then, becomes a symbol for storytelling in both a literal and more metaphoric sense. Good storytelling, as well as good juggling, entails managing many different elements in such a way as to make them all make sense, both individually and in the context of the greater narrative. This is something that Rashid (and, it should be noted, Rushdie himself) does with his storytelling.
The timeline below shows where the symbol Juggling appears in Haroun and the Sea of Stories. The colored dots and icons indicate which themes are associated with that appearance.
Chapter 1: The Shah of Blah
Chapter 6: The Spy's Story
...takes in the view and Blabbermouth pulls three balls from her pocket and begins to juggle. She's a skilled juggler, and keeps adding balls until she's reached 11. Haroun thinks that... (full context)
Chapter 11: Princess Batcheat
...seems willing to argue, but Bolo cries that chivalry demands that they watch the Chupwala juggle. The Chupwala pulls a variety of objects from his cloak pockets and begins to juggle... (full context)