Keeping with this discussion, an understanding of market power and its impact on price and quantity are important. Market power is important in determining when a firm has monopoly power and when to enforce anti-trust policies. When a firm has market power, its actions and decisions impact the price and quantity of the goods it sells in the market. How do firms attempt to gain market power? Why would a firm in a perfectly competitive firm attempt to differentiate its good and move the market towards monopolistic competition?