SmartSVN comes with a couple pre-installed plugins, based on SmartSVN's Plugin-API Plugins contribute additional functionality to SmartSVN which can be helpful to certain users but in general is not required by most users; resp. functionality which is not primarily concerned with SVN.
Plugins are deployed as separate JAR files which are located in plugins sub-directory in SmartSVN's installation directory. A plugin can be disabled simply by removing the corresponding JAR file from this directory.