Sailing is the only way to get to much of the map, unless you happen to have a randomly generated map that has land all really close together.

Once you get anything better than a raft, it will typically be faster as well if you get any amount of wind behind you, and helps with some major runs for heavy stuff like metal as it has a hold on the ship that can store that heavy gear to help you transport it back wherever you need to go.

That said, it also can be safer at certain points with the raft to sail at a safe distance from land, and can get a decent speed in the right conditions.