Joomla! multisites manager allows you to have multiple sites running in a single hosting account and share database data between different Joomla! sites. Single login/logout on websites.
No hacks of core files are required and no Joomla! core files are patched.*
Ability to use database content, users (with Community Builder and JomSocial support) from other sites.
You can have many Joomla! websites using a single hosting account, with same users and JomSocial contents but with different template style etc.
You can easily replicate your current website into other website without building new hosting account!
INFO