Why do we need to do this?

As in a conversation between "real" humans, the caller may need to keep the other person waiting, to find a document, to answer someone... To do this, the caller warns the other person by asking them to wait a few moments. Well, this also happens when you are talking to a bot!

How do you allow the bot to wait when the caller asks for it?

Nothing... I mean normally! It is provided by default at the creation of each bot, the script contains in its Fallback, a special "Wait" intent that allows to wait for the caller to return when he wants to speak again. The bot thus waits until he speaks again and resumes the conversation without repeating the question. The question is repeated if the caller requests it (Wait & repeat can be managed at the same time).