Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 75%, so most parameters are already documented, but the description adds meaning by grouping service_id/slot_id/starts_at as 'the time' and including action_id in the call shape, plus stressing starts_at must match the returned value exactly. It adds value over the schema without fully substituting for the undocumented action_id semantics.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.