The correct answer is C. Correlating events across multiple sources involves the SIEM's capability to collect data from various systems and find patterns or anomalies that could indicate a security incident. It is most effective for quick detection and analysis because it filters out noise and false positives, highlighting the most critical issues that require attention. While increasing storage capacity or buying a faster processing server may seem beneficial, they do not directly contribute to the detection or analysis of security incidents and might only provide additional resource overheads. Scheduled reports are useful for routine checks but are not the best approach for immediate detection.