When it has congested status, it prevents character creation and transfers to try and get people to make characters on other worlds.

This is done when it's stretched to its absolute limits. It started back when everyone went to Balmung. Many people didn't care about going to the other worlds. They wanted to be on Balmung so much for the RP community that they would go as far as to do a paid transfer to circumvent the new character limits that were in place most of the time. I made a linkshell on there and it filled up with over 100 people, mostly new transfers, in just 2 days. It was at that moment I knew Balmung was a bubble that was going to burst and that SE needed to do something.

And they did. They made a new status called "Congested" status that not only absolutely prevents new character creation, but also prevents transfers. Although this had a very bad effect on the server, preventing new players which are a necessary part of the game, it helped a lot by motivating people to go to other worlds to play with their friends. World Visit helped as well because there's not as much reason to be on Balmung if you can simply world visit to it anyway.

And now, this status is useful at a time when Aether and Crystal are extremely congested while Dynamis is in need of people to further populate it.