They used to serve other purposes. The old use as currency β give a card to get a card β has mostly vanished.
The biggest remaining purpose is to exchange contact information from someone, and often there are better ways. In these days a text message or social media contact is as good or better. If you ask for contact information and whip out your phone, they may hand you a business card, but you don't need to give them a card in exchange.
If you want to have a card with you for exchanging information, go for it. But the days where you needed to bring 200+ cards which you know full well are going to be thrown out are long gone. You can, you no longer need to.