Every JAR file in the glassfish/modules directory adds to the overhead of server startup. So JAR files that are not OSGi modules should not be in that directory.
This issue is for moving admin-cli.jar out of glassfish/modules, possibly to the glassfish/lib/client directory.
It is unclear how much of a performance gain would result from this. This bundle is in the Active state, so there is something in it that is getting used by the server. However, this bundle is supposed to just be used by the nadmin/asadmin CLI.