Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the full safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's added value is the payoff of the response: the policy content plus an 'official policy link'. That return-content hint is useful given there is no output schema, though it stops short of noting behavior when a venue has no published policy.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.