Monitoring insider trading activity is important because it provides insights into the confidence levels of a company's insiders, such as executives and directors, regarding the company's future prospects. Insider buying can signal optimism, suggesting the stock may be undervalued, while insider selling might raise questions about the stock's upcoming performance. However, it's essential to consider that sales can also occur for personal financial reasons. Insider trading activity is a valuable indicator that, when combined with other data, can help inform investment decisions.