It serves the same purpose as asking customers "are you a terrorist" -- it creates an easily prosecutable offence.

Could you expand on why is it easily prosecutable?

I sense that it has something to do with lying in documents.

But hypothetically: if I write “no”. Proof of lying requires proof of terrorism. (At which point you did all the job of proving terorism, despite the document)

Is terrorism not already an easily prosecutable offense?