In docs:
"The key component there is a custom LogManager implementation, that is
aware of different web applications running on Tomcat
(and their different class loaders)."
But each web application has own appenders in log4.properties (xml). So different applications have different logs. Why we need again LogManager that is aware of different web applications?
Because you might have (actually will have in most cases, think Apache Commons) identical classes in different web apps. And you still want the log entries to end up in the right file.