Optimizely Customized Commerce comes with a logging API, which is an abstraction for writing log messages from the system. Logging is useful when you troubleshoot and locate application problems.
Customized Commerce also uses EPiServer.Logging, which is used internally by the Optimizely assemblies for all logging. However, a third-party product or implementation can use the API. When you create new sites using the Visual Studio integration, the EPiServer.Logging.Log4Net package is installed by default, which is the log4net implementation of the API.