Beta testing allows the site to undergo usability testing with real users in a live environment. They provide feedback so that any malfunctions that they find can be reported and fixed before the site is launched.

The beta version is the first version released outside the organization or community that develops the software, for the purpose of evaluation or real-world testing…

Using customers as free testers who feedback real data into the development process allows a faster iteration of the design to occur in real time. Often their observations or suggestions would be difficult to replicate in a usabilty lab. It is also a way of engaging with a site’s users and fosters a feeling of collaboration.