I've come across this construct on Stack Overflow, in the title of the question "What use is lambda in PHP?"
To me this was an error, so I edited the question changing the title to "What is lambda used for in PHP?" and corrected some other stuff on the question.
Later the original poster changed the title back saying it was not an error and that it changed the voice of the phrase.
I'm not a native English speaker but consider myself pretty fluent in the language, and I have never seen this construct. Not that I remember, at least.
What does it mean?