It is often convenient to have multiple environments at one's disposal. For example, it may not be obvious that a piece of software will work the same on different Linux distributions. The same is true of different versions of a distribution, library, or service. It might be necessary to test a piece of software in the various environments in which it is expected to run.
Normally, in order to check this, it is necessary to have multiple machines or a single multi-boot machine. However, this port makes it possible to run different environments in different virtual machines, allowing testing in those environments to happen on a single physical machine without rebooting it.