I cannot think of a single app where there is a button to shut down the computer.
Nero has an option to shutdown the computer after it's done burning a CD/DVD. But yeah, I can't really think of a situation where its useful either. Otherwise, point out that shutting the computer down every night is not necessary, and possibly even a bad thing.
First take his money, then write the program, then tell him that using it is probably not a good idea. :o>