If your security model depends on a signing key, then protecting that key is one of the most important parts of the whole system.
Keeping the private signing key offline is powerful because it reduces the number of places where the key can be exposed. The fewer systems that can reach it, the smaller the attack surface.
Why this is better than normal backend trust
Many services assume the backend is always trustworthy. But if a backend is ever compromised, an attacker can often change data, configuration, or routing. An offline signing model limits what an attacker can do without the signing key itself.
That does not make the system magical. It just means the trust model is much stronger than 'the API returned it, so we accepted it.'
What users should understand
The main point is simple: if the signing key is kept offline, it becomes much harder for an attacker to produce something the app will trust.
That is the difference between relying on assumptions and relying on verification.