Big difference is the obvious: space between boards lets water flow between boards. A regular deck does not need to slope away from the house since it can not hold water. A tongue in grove deck needs slope away from the house or it will risk water being driven against the house and leaking in or puddles forming on deck with minor levelness imperfections. Slope is easier to achieve if deck is not deep. On deeper deck, generally avoid tongue in grove, on shallow deck it is an option--but a very slight slope is needed.