We rather like to have thoughts and such written out that are not fully revealed by the spoken words. A character asks about future plans, yet merely thinks about one of the worse what-if scenarios. That provides the other player with material to work out future actions/dialogue from, despite nothing about actually having been stated out loud.

Even a character choosing not to speak a reply is useful for dialogue in a story. Sometimes the best piece in a dialogue can be that which isn't spoken, rather than what is.