Any complex website that needs updating has to be tested without affecting the users of the live site.
The challenge then is how to replicate the changes made on your test site on the live site.
If all the changes are in code then version control systems such as svn and cvs solve this problem very neatly.
But with a CMS such as Drupal some changes are inevitably required in the database.
Managing these changes without affecting the site content can be tricky.
editors to add information about new projects, partnerships, news and so on. These elements are automatically cross-referenced and appropriate articles highlighted on the home page.