In most cases, reservation is not mandatory but highly recommended! By buying your tickets in advance, it allows the carriers to plan adapted transport and ensures you a seat on one of the day's routes.
And what's more, it's often cheaper 😉.
Please note: if you are going to one of the airports, you must book your trip from resort 48 hours in advance!
Specific cases: some journeys are carried out by school lines or within the framework of "Transport on Demand". Booking on these lines is obligatory (48 hours in advance and no later than Friday midday for the weekend and on Mondays). They are indicated by an exclamation mark when you select your schedule.