Owning a card means you can impact the career of that player. You earn points based on their performances in matches, and can use those points to train players or boost their performances in important upcoming matches. You also get a say in transfers and what shirt your player may be wearing next season.
Each player card is unique, granting a one-of-10000 share in that player. Each card number is only issued once and you own a piece of that player alongside other fans.
Owning a card also allows you to enter that player into your Pro Fantasy team for a chance to win weekly prizes.