What is THETA fuel used for?

Could you please elaborate on the utilization of THETA fuel? I'm particularly interested in understanding its key functions and applications within the THETA network. Is it primarily used for transactions, staking, or perhaps for powering decentralized applications? Could you also provide some insight into how THETA fuel contributes to the overall scalability and efficiency of the network? Additionally, are there any specific scenarios or use cases where THETA fuel plays a pivotal role? Thank you for taking the time to explain this to me.