Booking regional train tickets in advance for the journey from Pisa to Florence is generally not strictly required, as regional Trenitalia trains run frequently throughout the day, and unreserved tickets maintain a fixed price regardless of when they are purchased. However, booking online or via the app beforehand can save time at the station ticket kiosks. Once you validate a physical regional ticket at the station stamping machines before boarding, you can board any scheduled regional train on that route.