The article said secure communication with other EU bodies was a use case.

If you work with lots of other entities who want full control over their own comms (e.g. other governments, other departments, other EU entities like European Parliament and Council, the UN, NATO, etc) then decentralisation or federation is a big deal.

In the public sector it's basically a requirement: it's bananas if your country's critical infrastructure ends up dependent on some a product effectively controlled by another country (e.g. Teams) - and you obviously want to be able to communicate with other govt entities rather than being stuck in an island.

Then it's a natural extension to the private sector - although for now, it feels more folks are on the "nobody got sacked for using Teams" train.