It’s expensive to self-host, and centralized if using Matrix.org. It has its uses, but XMPP MUCs have a lot of overlapping features & Prosody/ejabbard can run on a potato by comparison.
It might be expensive for an organization to host, but for individual / small groups it can be as low as $6/mo. I've been running a small Matrix server on a DigitalOcean droplet for years now, and the $6/mo plan has been working fine for 5 users, and three bridges running on that server.
I believe all messages/multimedia from all users & the history all the rooms & private messages need to be mirrored which can end up being a lot even with a few users depending on what they’ve joined. If my understand is wrong tho, I’d like to know so I’m not running around with this notion.
