What are the practical uses and significance of Sai Baba's Udi as described in the texts?

Based on the accounts in Chapter 35, Sai Baba's Udi, or sacred ash, has multiple significant functions. Firstly, it acts as a form of blessing and permission. The text explicitly states that receiving the Udi Prasad along with a blessing serves as Baba's permission for a devotee to depart from Shirdi. As Chapter 35 explains, transgressing this and leaving by one's own will could invite obstacles. Secondly, the Udi possesses protective and healing qualities. Chapter 35 recounts the story of a gentleman from Bandra who was tormented by bad dreams. A devotee advised him to apply the Udi to his head and place a packet under his pillow while remembering Shri Sai. This remedy immediately removed the trouble, demonstrating the Udi's 'natural tendency' to alleviate suffering and provide peace.