For Cinque Terre, even at that time of year, most people who write in here are booking ahead, if they know the dates they are going to be there. The usual explanation for not booking ahead is for people who do not know their dates and want to retain flexibility about what days they show up. If you already know your days, and apparently you do, there is no advantage in failing to book ahead. And the disadvantage is that the best rates and locations are already booked up by people who did book ahead; and you spend a significant part of your day and energy concerned about where you are going to sleep. These are small villages with a limited number of rooms. Once they are gone on, or you cannot locate efficiently the one or two rooms that are left, you have a real problem because you can't just get back in your car and go to the next destination.