Airline cards offer a variety of benefits such as lounge access, free checked bags, priority check in, priority boarding and in-flight purchase discounts.
Just know, that even if you are flying on a reward, you will still get the card’s travel benefits. When you book your reward ticket, the airline knows whether you are a cardholder based on your frequent flier number. You may want to have the card on you, just in case, but I have never needed it.