I'm trying to understand the process of visiting and leaving Shirdi. Is it true that you can't just leave whenever you want, and how does Udi fit into this?

According to Chapter 35, visiting and leaving Shirdi are not matters of one's own will but are governed by Sai Baba's grace. The text emphasizes, "No one comes unless I bring them," and similarly, one cannot leave without his explicit permission. Leaving by one's own will is said to bring dreadful interruptions and humiliation. The process of receiving permission is directly linked to Udi. A devotee would bow to Baba to ask for leave, and the blessing given along with the Udi Prasad served as the formal permission to depart. Therefore, the gift of Udi is not just a sacred ash but a crucial signal that your departure is sanctioned by Sai, ensuring a safe journey.