Final answer:
The key reason for periodic marginal analysis is to maximize profit, identifying the point at which the value of the marginal product equals the market wage to determine optimal employment levels.
Step-by-step explanation:
The most important reason for a firm to do a periodic marginal analysis is to maximize profit. Marginal analysis involves comparing the marginal revenue of producing one more unit of a good or service to its marginal cost. This method is crucial for decision-making as it helps determine the optimal level of production and employment that maximizes a firm's profit. When we apply this analysis to labor for a firm operating in a perfectly competitive labor market, we consider the value of the marginal product at each level of labor. The profit maximizing level of employment is reached when the value of the marginal product equals the market wage. If the going market wage is $12, the firm will hire workers up to the point where the value of the marginal product is $12. Any additional workers beyond this point would cost more than they contribute in revenue, thus not contributing to profit maximization.