Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate destructiveHint=true; the description adds valuable behavioral traits: the role requirement for the recipient, the 7-day expiration, and the ability to cancel. This goes beyond what annotations provide, though it doesn't detail the output state (covered by output schema).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.