The new Managed Disk feature in Azure, takes away Storage Accounts completely, because you are now managing a single resource for that disk connected to your VM, there are no Scale out limits for Managed Disks, with the previous storage account solution, you were advised by Microsoft not to overload more than 40 disks per storage account, Managed Disks completely takes that away, all you need to do is define the Disk Type and Size, and that’s it.

Uploading your own custom image is now even easier to managed through the portal with much more granular control.
With the managed disk solution, you can now take a snapshot of the managed disk for backup, or create a managed disk from the snapshot and attach it to a test virtual machine to troubleshoot.

These managed disk snapshots are a full point in time copy of the VM Managed Disk

Below is a simple and very effective PowerShell script which will convert your legacy deployed VM (which would be in a storage account) and convert that into a Managed Disk

$rgName = "RG-VMs"
$vmName = "VM-2016"

Stop-AzureRmVM -ResourceGroupName $rgName -Name $vmName -Force

ConvertTo-AzureRmVMManagedDisk -ResourceGroupName $rgName -VMName $vmName