The Trenitalia Pass allows travel on all the Trenitalia trains in Italy.
You only pay:
The Eurostar Italy surcharge ("Upgrade"), if using these trains Eurostar Italia (the upgrade also lets you book your seat, which, on Eurostar Italia trains, is always compulsory);
the couchette or bed place, if used Night Trains;
a special fare if using the Artesia train
Trenitalia Pass holders also have the right to benefits for accommodation in hotels, purchasing ferry tickets and much more besides.