Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose one important mutation behavior: the child layers are preserved and restored to the group's position rather than discarded. It says nothing about whether nested groups are recursively dissolved, what happens to the group layer itself, permission requirements, or error conditions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.