Please specify more what happens when not "specifying log4j2 related params"

If I do not "set the following JVM properties when running your code to ensure that the log4j2 JUL bridge works correctly:", what will happen ? Will - logging statement will be missed ? - it fail ins some form with an exception ? - redirection will fail ? it would be great if this library could guaranty that with a "single dependency", all logging goes to log4j2 (without doing anything else, like setting params) if possible.