Description
"Code guards are typically used to guard code that only needs to execute in support of logging, that otherwise introduces undesirable runtime overhead in the general case (logging disabled). Examples are multiple parameters, or expressions (e.g. string + " more") for parameters. Use the guard methods of the form log.is<Priority>() to verify that logging should be performed, before incurring the overhead of the logging method call. Yes, the logging methods will perform the same check, but only after resolving parameters."
(description extracted from http://jakarta.apache.org/commons/logging/guide.html#Code_Guards)