CComment docs
Content - CComment (joscomment)
This plugin is enabling the comment system in Articles (com_content), Virtuemart (com_virtuemart) & Matukio. When you create your articles, products or events you could use the following tags to control the execution of the comments:
{ccomment on} - this will enable the comment system independently of the ccomment configuration
{ccomment off }- this will disable the comment system independently of the ccomment configuration
{ccomment closed} - this will close the article, product or event for further commenting. Only comments that were previously posted will be visible. The user won't see the comment form for commenting
The On content prepare option applies only to com_content. By setting it to yes we will replace the {ccomment on|off|closed} tags with the actual code of the component. If it is set to no, then we will add the code for the component using the onAfterContent event. Only use this setting if you use the {ccomment on|off|closed} tags in your article all the time and you need to show the comments in a tab for example. More info in this forum thread.
If you are on joomla 2.5 make sure that you are using the latest version (at the time of writing this doc 2.5.11). There are bugs in older version of Joomla that can cause the plugin to not function properly.
On content prepare option is only respected in article single view. On featured or blog view we add the component code using the onAfterContent event.