VMs allow you to experiment with other operating systems.
They allow you to work safely with more reliability and security: VMs are essentially like working in a sandbox environment (see * note). Working within such a controlled environment when running programs is a good way to learn about operating systems (i.e. Linux). When you’re done evaluating or testing operating systems you can delete the VM or create a snapshot once everything’s been configured just in case anything goes wrong.
VMs also allow you to consolidate servers: Up to 10 applications can run on a single VM that may have required several physical servers to operate.
*A sandbox is a security mechanism for separating running programs. It is often used to execute untested or untrusted programs or code, possibly from unverified or untrusted third parties, suppliers, users or websites, without risking harm to the host machine or operating system.