When you have all content authors in one location, you can set up a single server with the DITAToo content repository and everyone will connect to that server.
All users can see the same files and folders and work on them simultaneously. This architecture works well as long all users are geographically close to the server. If all users are on the same local network, the network is fast, and the distances are short, then all users can enjoy virtually lagless environment.
However, as the number of users grows, and they reach for the server from more distant locations, lags start to appear. In extreme cases, when teams are located in different countries and have to communicate with a server that is located on the other side of the globe, delays may become intolerable. Now, when a user locks the entire repository for everyone just to modify a single file, this simple operation may take many seconds to complete, and chances are that other users wishing to write to the repository will have to wait too.
This picture shows a situation when teams from remote locations have to connect to a single content server.
This calls for of a different architecture, in which there would be more than one server. Those servers would be connected into a cluster and enable users from different parts of the world to work with a server that is much closer to their location, thus ensuring local speeds for everyone. The servers would silently communicate with each other, maintaining the same data on each server via the synchronization server. This is the DITAToo distributed architecture.
This picture shows the distributed architecture.
For example, if you have one team in the US, another one in Europe, and one more team in India, 3 separate content server will be set up so that each team would have their own local content server.