In monopolistic competition, where many firms sell differentiated products, advertising plays a crucial role in firms' strategies to distinguish their products from competitors.

Advertising costs have many advantages, such as product differentiation. Effective advertising can clearly differentiate a product from its competitors, creating perceived uniqueness and potentially reducing the elasticity of demand. They provide valuable information about product features, benefits, and improvements, aiding consumers in making informed purchasing decisions. Also, successful advertising can increase demand for a product, potentially leading to higher sales volumes and market share. This shifts the firm's demand curve to the right. It also fosters brand loyalty, reducing consumer sensitivity to price changes and protecting the firm from competitive pressures.

Another potential advantage is that strong brand recognition, achieved through advertising, can act as a barrier to entry for new firms.

However, significant advertising expenses can reduce a firm's net profits. The effectiveness of advertising can diminish over time, requiring continuous investment to maintain brand presence and consumer interest. In markets with excessive advertising, leading to an "arms race" where firms must spend more just to maintain their market position.

In summary, while advertising can differentiate products and inform consumers, leading to potential market advantages, it also carries the risk of high costs and diminishing returns, making strategic and efficient advertising crucial for firms in such markets.