I will be travelling by train from Cassis via Marseille to Cavaillon, then Cavaillon to Arles and back to Marseille. Is there any need to buy the train tickets in advance or is it best to purchase them at the train station-thanks.
Without checking schedule, I will give some general comments. The ONLY reason to buy tickets in advance, on-line is to take advantage of any discount that MAY be available. But the discount tickets will come with restrictions regarding changing and refunds. It is extremely rare for a train to sell out so you do not need to make reservations in advance for that reason. Finally, regional or local trains generally have open seating so you can always get on but may not always find a seat so again no advantage for advance purchase. For your traveling buying at the station is fine.