Hi Oscar and thanks for your question! Our ItaliaRail CEO answered this question a few months ago; I'll copy the relevant parts below:

There isn't usually much of an advantage with a rail pass over buying individual tickets within Italy - especially if you know your exact itinerary; expect to stick to it; and, are only traveling 2-3 times by train.
A rail pass can make sense in certain circumstances but it really depends on what your itinerary is.
The longer your stay in Italy and the more train travel days you use the more a rail pass may start to make better sense.
There are two options for rail passes in Italy - both available to Members through ItaliaRail:
a Eurail Italy pass - valid for 3,4,5,6 or 8 days of travel within a 30 day period.
a Trenitalia pass - biggest issue here is that they have a shorter validity compared to the Eurail (3 or 4 travel days within 7 days; 7 travel days within 15; or, 10 travel days within 30) compared to the Eurail (3-8 days within 30 days). Better priced and value but ONLY if you are traveling extensively within a relatively limited amount of time. A Trenitalia Pass sometimes might make sense to consider if you are going to be traveling between Rome-Florence-Venice and your overall trip is between 8-10 days and you want to have maximum flexibility - even then it's debatable.
Bottom line - it is usually better to buy individual tickets in advance rather than a rail pass for Italy; but it depends on your exact itinerary.

If you'd like personalized assistance planning and booking your rail travel, please contact a member of our Traveler Experience Team via email at info@italiarail.com or by calling 1 (877) 375-7245 (M-F 9 am to 5 pm) or clicking the green \"Help\" button in the lower-left corner of our Contact Us page. One of our agents will be happy to help you compare your options to find the best solution for your travel.

Have a wonderful time in Italy and thanks for being a member of our community!

I am traveling to south of Italy starting from Rome, and I want to know if its worth to buy the rail pass. Wwe are traveling 2 adults and 2 children under 12.