In Cannes, there is a beach walking distance from the port. You can walk around there. Rome and Florence are a good way from the respective ports. If that's where you want to do, planning is necessary. You probably should not count on booking an excursion just walking off the ship. In Naples, what do you want to do? For anything other than going into Naples, planning is necessary. You can DIY to the major destinations, but you can't count on booking something at the port. You can walk around Palma right off the ship.