- Control
What has driven enterprises to move towards open source is not the cost savings, not the community, not the name of the vendor. It's control. When you are running open source you control your own code. You also control the code budget.
- Highly customised interface
In open source, you get a highly customized interface which if done well, can result in huge gains for the customer.
- Plenty of plugins to choose from
For extending the functionality of your site like adding a bulletin board or a shopping cart system, using softwares like Joomla or Drupal can be of great help as there are plenty of plugins to choose from. This is because, in an in house CMS, you are limited to what the web designer can provide.
- Portability
If you are using open-source system, you can take the website with you if you choose to move on.