The functions are basically as described, you get a slightly larger battery so it has increased capacity for powering stuff, you get a higher capacity alternator so it is capable of supplying more current to recharge your onboard batteries or power 3rd party equipment and finally the terminal block is literally a set of connections that output a variety of things from the van like voltage/lighting functions/engine run signal etc
The terminal block is designed to provide a single handy connection point for conversion works after manufacture and will be mainly utilised by companies converting the van into an ambulance or an RAC truck or a delivery van etc etc etc, theres not much that would interest an end user there other than an ignition live/engine run signal possibly ?