Rather it's convenient or not depends on how far you're going. When I lived in Italy, I preferred train for trips less than about 6 hours because you don't have to deal with travel between cities and airports (stations are near the city center), there's no need to arrive two or three hours early, no check in/security and no waiting for baggage on arrival. With shorter trips you can actually get to your destination as soon or earlier by train. It's also more comfortable.. However, flying is much faster for long trips and more relaxing than driving.

I don't find it all that convenient. It often takes me out of my way somewhat, actually, and involves an awful lot of hassle and waiting. It is more convenient to drive (I walk out my door and hop into the car, and go-that is pretty convenient), but sometimes driving is simply too slow (takes too long).

Because the flight comes with services. People taking care of your luggage, food and snacks, a chance to rest, and the speed with which you get from point A to B (not including waits of course).

It's much faster.

It's much faster.

Because sea travel is inexorably slow.