Without this extension we would have to maintain (update!) multiple Joomla! installations and all the plug-ins in those websites. Given the frequent updates of Joomla! it would take a lot of time to update all the websites and would pose a lot of update problems risks.
Joomla Multiple Sites (JMS) enables having a single Joomla! installation and single plug-ins installation and run as much websites as we want with simple update process for the websites. The work involved in replicating what JMS does would simply be too great to justify the use of Joomla!.
The support provided is near instantaneous and we always get what we need.
We highly recommend this extension for anyone running 2 or more websites or planning to do so in the future.