As the closest technology to existing on-premise systems, VMs are best placed for use cases requiring either fast migration to the cloud or those legacy systems that cannot run on other services without reworking the application.
The ability to quickly provision, test, and destroy a VM makes them ideal for testing and developing products, especially when you need to ascertain how a particular piece of software works on different operating systems.
Sometimes a solution may have stringent requirements around security in that they cannot use shared compute. Running such applications on VMs helps ensure processing is not shared. Through the use of dedicated hosts, you can even provision your physical hardware to run those VMs on.