This is the Meet Magento New York 2014 talk "Saving time and money with Vagrant" with Tim Broder. Vagrant lets you QA server configurations for your Magento site just like you do your code.
Vagrant lets you setup a dev environment for a new project in 5-6 commands and about 10 minutes.
Everyone benefits from Vagrant - solo developers, startups, agencies, large scale businesses.
Vagrant helps with complex stacks - such as using Solr, Varnish, etc. - getting it all setup in one Vagrant box saves a lot of time.
Chef, Puppet, Docker, Ansible and Salt are all options for provisioning Vagrant boxes.
Slides, examples and much more are available here.