It is one of the five canons of classical rhetoric (the others being inventio, dispositio, elocutio, and memoria) that concern the crafting and delivery of speeches.
[1] As with memoria, the canon that dealt with the memorization of speeches, pronuntiatio was not extensively written about in Classical texts on rhetoric.
Its importance declined even more, once the written word became the focus of rhetoric, although after the eighteenth century it again saw more interest in the works of men such as Gilbert Austin.
This excerpt from Quintilian's Institutio oratoria provides an example of the types of advice provided by rhetoricians: While the content, structure, and style of oration were (and continue to be) the most important elements of oratory, effective delivery enhances its persuasive power, and poor delivery detracts greatly from its intended effect.
Punctuation is useful in written discourse because it marks the end of a thought and allows the reader to pause and process the information.