Rule 2 of 8 · Chapter I — Portal Discipline
Resource groups are blast radii — group by lifecycle, not by type.
Why this rule exists
The resource group is the unit of delete, of RBAC, and of cost rollup. A group holding "all the databases" cannot be safely deleted, granted, or costed for any one system.
In practice
One group per system per environment (myapp-prod-rg). If two resources die together, they live together; if not, separate groups.