The beta comes in both basic and PRO versions. You have to be a PRO customer to get the PRO beta.

Beta versions are versions that have the newest features, but aren't quite ready for "prime time" yet. They've been tested in the LW lab, but they haven't been tested on the millions of possible software configurations that are out there "in the wild".

If you run a beta version, you get the latest features, but the downside is that the latest features might not work properly with your setup. The LW developers use bug reports from the beta version and keep improving the features.

Once the problems with the beta are ironed out, it gets re-released as the official LW version.

If you want to get the latest features before everyone else (or if you just want to help the latest LW features make it into the official version faster), and are willing to deal with the possibility of the newest features not working (or the latest features causing problems with existing features), then you might like the beta version.