For some reason, I've found some confusion on travel webites concerning the exact nature of "premium" class on the Trenitalia Frecciarossa trains. This is nothing more than "standard" class (or second class on the other Frecce trains) with leather seats, a complimentary Italian-language newspaper on morning departures, and the welcome drink/snack!!!! The very small extra charge pays for these products. It's a gimmick, and indeed, there is ordinarily only one "premium" railcar on the convoy. "Business" class is entirely a different matter, like first class on the other Frecce trains. The extra change for business/first class is often characterized by travelers as a waste of money, although just about everyone recognizes the slight upgrade in seating arrangements, and "special occasions" often justify the extra expense. Additionally, as Larry notes above, sometimes the extra cost is minimal, depending on the ticket type and when purchased.
Three takeaway recommendations:
1. Always check schedules and fares for Italo Treno on routes shared with Trenitalia. Italo often has lower fares;
2. Always check the promotions pages for both Trenitalia and Italo Treno, as new, seasonal and temporary promotions pop up from time to time;
3. On certain routes which also offer Trenitalia Frecciabianca and/or Intercity trains (e.g. Rome to Naples or Salerno), check fares and schedules for these trains, as you may save money compared to the faster trains; and
4. On certain routes which also offer Trenitalia unreserved regionale trains (e.g. Milan to Verona; Verona to Venice; Venice to Bologna; Florence to Rome; Rome to Naples), check fares and schedules for these slow trains, as you may save lots of money compared to the fare for a fast train when the ticket is purchased at the last moment.