I believe you typically get the money withheld, and if when you file are determined not to have any tax liability, you get a refund between what you paid and what you owe. That’s just like anyone else, but that second number happens to be zero. I swear there’s an option in a W4 that you had/expect to have your tax liability be zero as well, but of course if you turn out to be wrong you’re in for a world of hurt