• Azure Resource Manager is the control plane of Azure

You might want an additional subscription to avoid reaching subscription limits, to create separate environments for billing and security, or to isolate data for compliance reasons.

It is not enough to grant a user the Global Admin role in AAD to give them access to a subscription. They must also be assigned an RBAC role (e.g. Owner, Contributor, Reader, etc).

• Management groups (MG) provide a governance scope above subscriptions
• MGs are a way to group subscriptions
• MGs allow budgets, RBAC roles and policies to be applied to them and the subscriptions they contain