You might have anticipated more exciting things than playing cards when you picked up Star Wars Outlaws, but lemme tell ya, Kessel Sabacc can be as thrilling as blasting stormtroopers or punching Syndicate members in the face. For one, it's a great way of making credits without having to do too much work, similar to the Fathier races.
Your first chance to play Sabacc comes when you arrive in Mirogana, and if you get on good terms with the Pykes, you'll be able to access their district cardroom for even more rewards.