Diagramming sentences provides a visual way to understand sentence structure by placing parts like subjects and verbs in relation to each other. Students who learn diagramming gain a clearer understanding of how sentences are constructed and how meaning branches out through different parts. The document then provides examples of diagramming different sentence structures like simple sentences, sentences with modifiers, objects, nouns/adjectives, compound subjects/verbs, prepositional phrases, clauses, and complex sentences to illustrate how diagramming visually depicts these relationships.