Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare readOnlyHint=false, destructiveHint=false, openWorldHint=true, so the agent knows this is a non-destructive mutation against an external system. The description adds nothing beyond that: no statement of which members are affected, how they are identified, whether it requires an admin token, or what happens to already-active members.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.