It's also for logging:

    log.debug(f"The value of counter was {counter}, the nonce was {nonce}")

builds a new string every time the interpreter hits this line. Whereas

    log.debug(t"The value of counter was {counter}, the nonce was {nonce}")

passes a Template to the debug() function that bails out if debug mode is not on and doesn't build a string.

Could also be used to prevent html injection.

It's for SQL, HTML, and shell. But idk how solving injection, a top on the OWASP list forever is considered "overkill".