The scgi handler allows Cherokee to communicate with SCGI programs. The configuration parameters are exactly the same from the FastCGI, so check that section of the documentation if you want to set up this handler.
The Simple Common Gateway Interface (SCGI) protocol is a project to replace CGI and FastCGI with a simpler protocol to both implement and manage.
In the end, SCGI offers the same performance as FastCGI (and better than other methods), offers cross platform simultaneous support and is simple to install, run, and configure.
It also supports simplified clustering on most POSIX systems for that extra boost in concurrency, but whether you use it or not will be mostly determined by your personal taste and experience.