Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint and openWorldHint, and the closing "Public, read-only" largely restates that. The description still adds real value by defining each status bucket (open orders buyers can take, being paid out, done) and by disclosing that amounts are SUN-scaled and estimateCompletionTime is in seconds.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.