Any speech, performance, presentation, toast, congratulatory message, or declaration of love is a monologue. Rhetoric, an applied science on expedient communication, is engaged with monologues (as well as dialogues).
As it is a science, rhetoric has quite strict rules and laws proven by practice and history starting from Aristotle. By breaking these laws, you will not be able to give your speech the effect you want and achieve your goals. If you don’t have goals you don’t need rhetoric. A speaker does not want to just speak «beautifully». A speaker wants to put a certain idea in people’s heads and push them to some action. The speaker wants to control people.