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The game appears in your single player game list so you can play it without being connected to the server. This has many advantages.

1) Good if you are playing on a laptop.
2) Good if you are playing in a place where internet access is billed by the minute.
3) Keeps you from accidentally submitting your turn and causing the game to host before you are ready.
4) Allows you to play your turn in multiple sessions.

It's so useful it ought to be in the official documentation, how and why to do it.