From fireeye.fr
To understand what a threat actor did on a Windows system, analysts often turn to the tried and true sources of historical endpoint artifacts such as the Master File Table (MFT), registry hives, and Application Compatibility Cache (AppCompat). However, these evidence sources were not designed with detection or incident response in mind; crucial details may be omitted or cleared through anti-forensic methods. By looking at historical evidence alone, an analyst may not see the full story.
Real-time events can be thought of as forensic artifacts specifically designed for detection and incident response, implemented through Enterprise Detection and Response (EDR) solutions or enhanced logging implementations like Sysmon. During active-attacker endpoint investigations, FireEye Mandiant has found real-time events to be useful in filling in the gaps of what an attacker did. These events record different types of system activities such as process execution, file write activity, network connections, and more.