The way I understand it is you can host your own relay which you can use for all incoming messages. But it’s all encrypted anyway. And instead of being centralized all in one place like Signal, which is all encrypted too, it’s spread to whoever wants to run a relay. And its simpler to use and run than Matrix. Messages also get sent back and forth to random relays (if your peer doesn’t have his own relay) to improve privacy, in case someone cracks the messages? I’m not an IT guy though, I’m just learning about all this recently.