There are many cases where it would be handy to group log events on some application specific information (e.g. placed in the MDC). Examples are

• Collecting all user session interaction loggings into a separate file
• Collecting all log entries related to a specific client machine into a separate file
• Collecting the entire lifecycle of an entity (long-lived order, process etc) into a separate file

This could perhaps be implemented with a LogFilePolicyClass that would return the correct (existing or fresh) file based on the MDC data?