This is used in the build.xml file generated by a Netbeans project, to override the default clean-up behaviour that deletes the 'build' and 'dist' folders. In case these folders are to be maintained in SVN, the following ensures that only the contents of the folders are cleared, leaving the SVN information intact.

Of course, the easiest option is to NOT check in the 'build' and 'dist' folders :)