Typically, however, there are benefits that come with owning a card beyond earning miles.
For instance, many cards offer special companion fares that let you get an annual free or a discounted flight with the purchase of a ticket. Or, you might get a certain number of free checked bags for each flight.
Keep in mind, though, that some airlines will restrict that benefit, such as only allowing it for certain seats and destinations.
Nevertheless, these benefits can be valuable to frequent travelers. The important thing is to weigh the value of those extras — and any miles you earn for purchases — against the yearly fee you pay.