Sarah is a portfolio manager at a mid-sized investment firm. She has constructed a diversified portfolio that focuses on large-cap equities and bonds over a five-year horizon. To evaluate the performance of her portfolio, she chose a benchmark composed of 70% S&P 500 Index and 30% Bloomberg Barclays U.S. Aggregate Bond Index. Sarah has recently read an article suggesting that using a composite benchmark might not accurately reflect the unique risk and return characteristics of her portfolio.
Which of the following statements provides the best rationale for the appropriateness of using the selected benchmark to evaluate Sarah's portfolio performance?