It's scoping the function to the script that it's in. It's actually a really unusual practice – I'm not sure I've seen anyone do that. You might ask Ed (the author) why he chose to do that. Overall it's kind of chock-full of less-than-good practices – the name doesn't follow naming conventions, the parameter declaration is the truncated kind, and it's outputting text rather than a value. I'm not sure what the context was within the book, but it's not how I'd normally expect a PowerShell function to be written.