Normally HQ loads every plugin available. You might disable some plugins that you do not need or plugins for software which is not available on your platform.
This is the full list of all currently shipped plugins:
activemq alfresco apache bind coldfusion db2 dotnet exchange geronimo glassfish groovy-scripting hqagent hq-internal iis informix iplanet jboss jetty jmx memcached mqseries mssql mysql nagios netdevice netservices ntds ntp oc4j openldap oracle perlbal postfix postgresql resin samba sendmail servlet sqlquery sybase system tomcat vim vmware weblogic websphere xen zimbra
For example on non-MS Windows platforms it makes sense to add the following line to your agent.properties file to blacklist the plugins:
plugins.exclude=exchange,iis,dotnet,mssql
It saves you some memory and maybe some CPU time for autodiscovery every 15 minutes 
On virtual guests you could probably add the following line:
plugins.exclude=vmware,xen
Currently only blacklisting of plugins is possible. Don’t forget to include plugins if you change the software set on your server .
If you’re not sure what the plugin is for, don’t exclude it