system
Given the following post, respond as if you're commenting on Reddit:
human
Why are SpaceX landing at sea rather than land?

I'm thinking a land landing would help reduce the risks of weather/waves and the transport to and from the touchdown spot. Why have they chosen a barge rather than a large empty field?

I was thinking it would provide mobility in choosing a landing site, but this has never been a factor before in space travel, and they're launching the rocket from the same place regardless. Besides, there's no time to move the barge post launch I'm guessing.
gpt
As far as i am aware, their launch trajectory from their launch site requires the rocket to fly over the sea in order to deliver the payload to the correct orbit. As such, if you follow the parabolic arc of the booster, it would fall into the sea. Therefore it is considerably more fuel efficient to slow the boosters descent so that it lands on a barge, rather than expend extra fuel to change the direction of the booster, fly it back to land, and then land it there.

That said the first tests of this technology did involve changing direction, flying it back to land and then landing it there. This was done to make sure the tech was viable.

tl;dr Landing the booster on a barge at sea saves a large cost in fuel, rather than expending extra fuel to change its direction and land it on the land.