there is no difference between a guild board, and a world board.
in a guild board you can ask about, in game things,
you can do lotteries, you can say your guild is dominant, and anyone wants to enter your world must to pay your guild..
you can ask help for random things. Even offtopics things can be commented in the world board.
and the same rules are applied to guild boards.
I don't believe there is an specific subject you can talk in a guild, You can't talk in the world board..
sometimes people use the world board to solve guild problems