The first advantage is a fast and simple check-in (actually you check-in when booking a ticket). Secondly, you can take luggage into your car, including liquids and non-cabin-sized bags. Very convenient is that the departure and arrival railway stations are in the city center, so you save money and time, being able to get by metro to anywhere in the city. Convenient seats with individual tables allow you to work on your laptop or watch a movie all the time of the trip (without breaks for take-off and landing like on an airplane).