How does Ubuntu's indexation work on a virtual machine?

I have read on https://help.ubuntu.com/community/FindingFiles the following sentence: >Thankfully my computer indexes all my files every night while I sleep and I can search just the index, which will take only a few seconds, even on as an expansive a filesystem as mine. And I was just wondering how does it work on a virtual machine? Does it occur even though the VM is powered off?