Italy Eurail Pass

Rabin, for Rome to Florence, you will need to pay a supplemental fee of 10Euro to ride the high-speed Frecci train. Seat reservations come with payment of the supplemental fee. You just can get onto the train. For Florence to Pisa, almost all trains are Regionale-class trains. Your pass will get you on these trains. But why a pass? The fare is only about 12Euro one way. From Rome to Pompei, you are again subject to the 10Euro supplemental fee both ways from Rome to Naples and from Naples back to Rome. That's an extra 20Euro. For the journey from Naples to Pompei, this will be on the private Circumvesuviana train. They don't accept the Eurail pass. Fare is about 3Euro each way so it's really cheap.

Rabin, For the very few trips you'll be doing, I very much doubt that a Railpass would be the most cost effective method. As the previous reply mentioned, when riding on the premium trains such as the Freccia high speed, you MUST have a reservation which is specific to each train and departure time. Even with a Railpass, if you're caught without a valid reservation, you'll likely be fined on the spot and it's not cheap! Fines start at €50 pp. When using P-P tickets, the reservation is included with the ticket. Happy travels!

Most people who have posted on this site have recommended point to point train tickets as being much cheaper than a rail pass.
I would agree and found that I used the train a lot and still saved money over the cost of what I would have paid for a train pass (My trip was 3+ weeks).

Good for you for asking BEFORE you actually bought the railpass. As mentioned above, don't do it! P2P is cheaper in Italy over 95% of the time.

Just buying tickets in Italy would be cheaper than a rail pass.