Whenever I read books with illustrations in them, they can provide an invitation to the story that can enhance the reading experience. The illustrations can vary, as when they are small, such as when they introduce a new chapter (above the text), or they can be on a separate page–interspersed throughout the novel. Sometimes they can leave you wondering if what you imagined matches the visuals that were described, though this can depend on the artist’s interpretation.
Comic books (or graphic novels) tell the story through visuals and the text rather supplements them, as there can be pages without texts. But with novels, in which there are tens of thousands of words, the visuals tend to complement the story, like providing cues for the descriptions, as when films have music that provides cues in certain scenes.
Not that stories must have illustrations, but they’re like extras, as when non-fiction books have artifact-like photographs of historical places or people. Whether the book illustrations are detailed like paintings, or as simple as small sketches, they can enhance the experience, or leaving you wondering if what you imagined matched what was described.
Fallton Havenstonne 