What many people don't realize is that Chrome is just the beginning, the first branch on a very large tree of code that spans numerous development milestones. There's the Chrome that people use and on a daily basis, and then there's everything else. The good stuff — like Android link push and extension sync — doesn't always make it into the stable builds as early as we'd like, and until it does, Chrome's many development branches are the place to find them.
As Google describes it, the beta branch allows users to "try out the newest tools while they're a little rough around the edges." Features that appear in beta builds are now officially part of the Chrome roadmap, but require a wider user test base to ensure they are ready for prime-time. Stability for core components is usually not an issue here, but tread carefully where new features and settings are concerned.