There are several levels of information that can be recorded to the debug files. The debug level is set using the Debug Level attribute located at Configuration > Sites and Servers >server-name > General.
Off: No debug information is recorded.
Error: This level is used for production. During production, there should be no errors in the debug files.
Warning: This level allows Error and Warning debug messages to be written.
Message: This level allows detailed code tracing.
Warning and Message levels should not be used in production. They cause severe performance degradation and an abundance of debug messages.