Another way of saying it is: What do you guys do with cards that you already got? (This includes friend summons, minus the N cards, because I'm sure we all use them for training anyway)
Do you use them to level up the same card you have to raise their SA, sell them for Zeni (Although, why would we do that.), send them to Baba, or use them for the dupe system?
The one in bold is my answer.