We know Visual Studio Pro with MSDN gets you unlimited Windows Server (including Hyper-V for virtualisation) and unlimited SQL. This is a way of licensing Microsoft software in your on premises test and development environments.
You can now bring your own MSDN licences with you to Azure. This way the Microsoft software in your Windows and SQL VMs on Azure is already paid for and you pay the equivalent of Linux rates for Windows and SQL VMs on Azure. Azure charges per-minute for VMs (as apposed to AWS per hour) so the billing better suits spinning up boxes for automated testing where each test takes less then an hour.
More info here: https://azure.microsoft.com/en-us/offers/ms-azr-0059p/