CrossRoads:
I connect it because the Promini has the CTS pin grounded.
The FTDI Basic connects the CTS header pin to the FTDI CTS pin.So, used or not, that's the way I connect it, and I never have problems with USB/Serial interfacing.
Grounding it will not cause a problem, but it is not a requirement, it will work equally well unconnected, that was my only point.
Lefty