The CCGX's main job is system monitoring and display of system status to you, bringing everything into one place. It has some relays that can be setup to run certain functions (example auto gen start, plus more) and can save and send the info to the cloud.
It also can adjust some controls on the Multiplus - incoming Amps on shore power, plus On/Off/Charge only.
It can be setup to control the charging and discharging - so all the attached devices don't exceed a certain charge rate. If connected to a BMS through a CAN-BUS the BMS can then control charging & discharging limits.
I haven't done anything with the raspberry pi - but I have seen several posts about it on the Victron Community.