I love the ability to assign users different levels/areas of access so that they can keep pages updated themselves and I'm not constantly updating something when someone emails me. This is an especially nice feature the bigger the pool of people who need to edit the page gets.
It's really nice that we've been able to allocate basic access to individuals so that we can focus on bigger issues and allow users to manage their own content. This is a great tool for a big organization.
Joomla! is great for giving lots of different users access to individual pages. If you want to manage a website but not have to receive countless emails requesting updates, you can give users the opportunity to make changes and updates themselves (and manage their access so that they can only edit what they're assigned). For an individual or a smaller company though, this may not be the best or simplest solution (something like Squarespace may better serve your needs).