List your reasons here:

• Software development and testing
  • If you frequently test hardware, operating systems, and applications, chances are you're likely to spend many frustrating hours rebooting while you troubleshoot problem apps, drivers, services, and patches.

• To sample alternative operating systems
  • Without committing a dedicated partition to the job. Since VMs can use virtual partitions (a partition that lives inside a file of dynamic or fixed size), you don't have to worry about reclaiming any hard drive space lost to experimentation.