the domestic flights within Italy see a mix of several types of travellers.
trunk routes like LIN
see a majority of business travellers, especially commuting on a daily basis (first flight in the morning, last flight in the evening).
most routes north to south have a huge VFR traffic along with businessmen.
of course there's a huge market for leisure and tourism, with Rome/Florence/Venice/Naples as the major airports from where to continue exploring our wonderful country.
furthermore the presence of several LCC, including brand-new Blue Express, which flies 3 times a day between MXP
with fares starting at Eur9.99 one way, along with the prospected new domestic network proposed by EasyJet and Ryanair, make it very very easy, and cheap, to fly domestically, also considering that the longest flight, Milan to Catania, is only 90 minutes long (well, Milan to Lampedusa is actually the longest non-stop, but is only a seasonal flight, in summer, and that's less than 2 hours), with an average of less than 1 hours on most routes (Rome is right at the center of Italy, a sort of hub and spoke network).