Can you give some examples of what you cannot do when you apply a read-only lock on an Azure resource group?

Read-only lock will prevent you from modifying any resources in the resource group.

Resource manager read-only locks usually apply only to operations that happen on the management plane. However, there are some exceptions to this - Read-only Locks can in some cases prevent access to the data plane, such example is Azure Storage.

As an example, for the resources in RG with read-only lock:

• You can't start/stop/restart a virtual machine because these operations require POST
• You can't create or delete a virtual machine
• You can't upload a blob to a storage account
• You can't list the keys in a storage account
• Visual Studio Server Explorer is prevented from displaying files for App Service because the interaction requires write access

Also when you put a lock to a subscription:

• Azure Advisor won't work because it is unable to store the results of its queries