Joomla Multi Sites allows multiple domain names or sites to have their own joomla configuration file using the same joomla installation. Possibility to share the users, and extensions like VirtueMart, Community Builder, JomSocial, ...
With this new feature you can share the joomla files and folders to create totally independent web sites.
This simply the maintenance of Joomla as you have only one instance to update for all the websites.
With Joomla Multi Sites you can both create website from the back-end and from the front-end. You can use website as template to create new slave site. When you decide to propose the creation of websites from the front-end, you can add a plugin to create a bridge with your own system to process the payment or whatever else.
As each website has its own joomla configuration.
You can decide to use:
- One database for all the websites. In this case, you must specify different database table prefix for each websites.
- Two databases (One master database and One slave database).
We have not tested our products with Multisites, so I can't guarantee will they work or not. However, from my understanding, Multisites component is not something that changes Joomla's behavior with templates.