You can now use Ephemeral OS disk in Azure Virtual Machine (Azure VM) when you are concern on the time taken to deploy at scale or reimage a virtual machine while not concerned with data (aka stateless workloads).
The good point with Ephemeral OS disk is there is no storage cost associate with and it supports both custom and marketplace images.
As this is a preview, you have to register first the required provider using Azure PowerShell or Azure Cli
Azure PowerShell
Register-AzResourceProvider -ProviderNamespace Microsoft.Compute
Register-AzProviderFeature –FeatureName LocalDiffDiskPreview -ProviderNamespace Microsoft.Compute
Azure Cli
az provider register –namespace Microsoft.Compute
az feature register –namespace Microsoft.Compute –name LocalDiffDiskPreview
Additional documentation is available here https://docs.microsoft.com/en-us/azure/virtual-machines/linux/ephemeral-os-disks?branch=pr-en-us-74400#scale-set-deployment