To me, the biggest benefit of a VM is that you've rendered the entire platform into just a few files. Once it's been virtualized, you can back up the entire platform easily. I've actually seriously considered running my default desktop as a large VM, so that if anything wanky happens with my hardware, it's a matter of fixing the HW, then restoring the VM, and moving on. No OS installation needed at all again. I haven't gone that route yet, though I have VMs that are dedicated as specifically used with my work. When/if I leave my current job, I'll wipe the VM, and build another for the next. That way there is no question of proprietary data hanging around from one contract to the next.
If you are using Virtual Box, you can also encrypt the VB files (whatever OS you are VBing).. ;^)
In my case, it’s encrypted x 2 (plus running sundboxie on the Win inside VB, so sandboxed x 2 also).