Casinos give away free stuff to members of their players clubs: free slots play, shorter lines, comps, travel, hosts, and events. The higher the tier level, and the greater the amount of recent play, the higher value of this free stuff.
But, the question must always be, is it anything you want? Stay focused on your gambling goals: entertainment, comps, making money, etc. Players clubs can support each of these goals, if you use them that way.