You don’t know where you stand in a particular poker hand and you are first to speak. In limit that is easy, bet and take a raise on the chin if necessary. In no limit and pot limit, generally you should also bet, but it doesn’t have to be the entire pot. By betting, you are crystallising the response of your opponents in your mind. If they call, it may be unclear where they stand. If one raises, then it is quite likely you are losing. Had you checked and the opponent bet, you are no nearer a solution to his holding than before. He may be bluffing, have a moderate hand or a monster.

As usual in poker, it is better to be the aggressor.