Managed Disks are a relatively new concept in Azure. Worth checking this out to understand what they are and why you’d choose that option.
In more complex scenarios, such as using Virtual Machine Scale Sets (VMSS) to create thousands of identical VMs, Managed Disks automate storage account scale management. Managed Disks now allow VMSS to scale up to one thousand VMs in a single set, 10 times more than was possible with unmanaged disks.
Source: What Are Azure Managed Disks?