Q: Why would I still use Affinity Groups in Azure now that Virtual Networks are region-based?
A: Affinity Groups were a critical requirements for Virtual Networks in the past because a Virtual Network was confined to a specific Affinity Group (no longer the case with regional Virtual Networks), which itself is a specific cluster of Azure servers. One key aspect of an Azure cluster (also called a stamp or scale-unit) is that all servers within the cluster are all the same hardware. This means an Affinity Group can still be useful if you want to ensure you're deployed to exactly the same type of hardware. However, remember that Microsoft levels the performance of dissimilar hardware anyway; therefore, you should always see performance parity, even across dissimilar hardware. If you want to be 100 percent sure you're on the same hardware type, then deploy to an Affinity Group.