’Cuz Pete Warden said so:
I have fallen in love with Vagrant over the last year, it turns an entire logical computer as a single unit of software. In simple terms, you can easily set up, run, and maintain a virtual machine image with all the frameworks and data dependencies pre-installed. You can wipe it, copy it to a different system, branch it to run experimental changes, keep multiple versions around, easily share it with other people, and quickly deploy multiple copies when you need to scale up. It’s as revolutionary as the introduction of distributed source control systems, you’re suddenly free to innovate because mistakes can be painlessly rolled back, and you can collaborate other people without worrying that anything will be overwritten.