Usage rate measures the percentage of a team's possessions that a player uses while they're on the court. It takes into account a player's field goal attempts, free throw attempts, and turnovers. It's important because it indicates how much of the team's offense runs through that player and can provide insight into their role on the team. The formula for usage rate is ((FGA + 0.44 * FTA + TO) * (Team Minutes / 5)) / (Player Minutes * (Team FGA + 0.44 * Team FTA + Team TO)).