[logn]

I think it's mostly from developers trying to use their target deployment environment or to use a common dev environment image. Others might like it as a nice way to sandbox different workspaces and for convenient functionality of taking snapshots you can revert to (like source control but for your whole machine). Also some orgs have their QA make extensive use of VMs to test different set ups and for reproducible bug reports.

[Tvorba]

Sure, I understand that, but a lot of people are talking about running multiple headless VM's at once and I can't really see any use cases outside of QC/QA environments. Even for people working on multiple projects at once (for multiple clients) it sounds like there is no real reason to run more than 2 at once (one for tools, the other for the server environment).