This early passage, along with others, establishes that Nick, Daisy, and Tom have a prior relationship, and that the Buchanans are wealthy. Nick describes them as people who gravitate towards polo-playing watering holes where rich people gather. More importantly, the passage introduces the theme of Tom and Daisy as restless and dissatisfied drifters who never stay in one place too long. Nick doesn't believe Daisy's assertion that she and Tom plan to settle permanently in Long Island. He says he has no sense of Daisy's emotional state, but he is convinced that the high point of the now thirty-year-old Tom's life occurred when he was a college football star. Nick surmises that Tom wanders because he is searching for the same elation or high ("dramatic turbulence") that football once gave him.
Along with introducing the concept of drifting, the passage introduces the idea of longing for a more glorious past, a very significant theme in the novel—it is exactly this desire to reclaim the past that motivates all of Gatsby's efforts.
As for drifting, Nick's intuition that Tom and Daisy won't stay put is borne out. After carelessly wrecking lives of those around them, the couple moves from the area, leaving a mess behind for others to clean up.