On our recent trip to Argentina, we all dutifully filled out the customs form they handed out on the plane. We all dutifully presented them to the immigration officer at passport control, who gave them back to us. The customs folks never asked for the forms, even though all bags were x-rayed.

I left the form in my passport and when departing, the passport control officer gave them back. So it's basically a sort of souvenir.

What is the purpose of these forms? Are they only supposed to be filled out by Argentine citizens and residents? Am I in trouble the next time I visit?