Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare non-read-only, non-destructive, non-idempotent, closed-world; the description meaningfully adds that the operation is asynchronous, spawns a background job, and sends an email to the current author — a side effect worth knowing. It stops short of saying whether repeated calls queue duplicate jobs (relevant given idempotentHint=false) or who 'the current author' resolves to.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.