When a game is played for free, that is the best time to learn the basics. The casino software can be tested extensively and there is no rush or pressure because money is not on the line yet. It’s a good time to learn how to play, the rules of the game, and anything else that must be known.
Not only that, free play is the best time to improve one’s skills at the game. That way, when a player plays the paid version, they know what they're doing and they will be good at the game when they play it. Plus, there doesn't need to be money on the line to enjoy playing the game itself.