Chapter 13 Logging and Reporting : Logging and reporting overview : FortiOS features available for logging : Event
  
Event
The event log records administration management as well as FortiGate system activity, such as when a configuration has changed, admin login, or high availability (HA) events occur. Event logs are an important log file to record because they record FortiGate system activity, which provides valuable information about how your FortiGate unit is performing.
Event logs help you in the following ways:
keeping track of configuration setting changes
IPsec negotiation, SSL VPN and tunnel activity
quarantine events, such as banned users
system performance
HA events and alerts
firewall authentication events
wireless events on models with WiFi capabilities
activities concerning modem and internet protocols L2TP, PPP and PPPoE
VIP activities
AMC disk’s bypass mode
VoIP activities that include SIP and SCCP protocols.
The FortiGate unit records event logs only when events are enabled.