Some Italo trains depart from Tiburtina. It depends on the destination. From Florence, it does part from Tiburtina. For other destinations there are now departures from Roma Termini, which is fairly new.

For me, having to arrive or depart from Tiburtina when going to Florence is a deal breaker. You have to take the Metro or a cab to get to or from Rome city center. I just don't like having to end my train ride on the periphery of the city, then having to take local transportation to go the rest of the way.

The paucity of stops or the poor location of their stops has generally kept me from using Italotreno. For example if you want to go from Milan to Venice, which I did two weeks ago, you can't do it. If you want to go from Milan to Torino you can do it, but the only place Italotren stops in Torino is Porta Susa, which like Tiburtina, is a train station pretty far away from the city center that requires you to then take a local train to get to the center of Torino.

It seems as if they are improving, as they now at least provide some good connections like Venice to Naples, Venice to Bologna, but as of now, until they get better train station locations I still find them to be inconvenient for most trips.