Your tone of voice, like your body language, can affect the meaning of the words you say. In successful communication, your tone of voice must match your message.
In a presentation, discussion or conversation you can change your tone at different stages to help keep your audience’s interest. A speech delivered in the same tone throughout (ie a monotone) will be boring as it seems to lack the necessary emotion and conviction.
Varying your tone will make your talk more engaging and convincing. Listen to Benedick’s speech from Act 2 Scene 3 of Shakespeare’s Much Ado About Nothing. This isn’t a natural conversation, but notice how the actor creates realism by varying his tone to show the character’s surprise and increasing enthusiasm for the idea that Beatrice just might actually love him.