My general understanding of binning in a nutshell: increased sensitivity, lower noise and faster frame rates.
I was informed from Sam that to enable binning in Firecapture you have to disable 'debayer'. After me spending some time setting up Firecapture I noticed I couldn't enable binning anymore and this was the reason.
If you intend to use Firecapture it is also recommended to run the latest beta release. I had some problems with the latest standard version. These problems were all resolved after following the beta upgrade instructions.
I'm all setup and ready to go with my 120MC - I just need a clear night!