As an Illustrator, you want to be sure to convey the activity or message of the story within each page. It's important to view both sides of the story, from the authors and illustrators point of view. But, what's important is how they piece together perfectly.
For example, here's the text a...nd illustration for Page 2 of "The Adventures of Daniel and Christen" by Author Delaine Taylor.
The boys quickly hid behind a large bush. Pirates came out of a cave yelling at each other about the directions of treasure. Each pirate had his own idea as to which way the group should travel for their search.
Did you notice the additional characters and items not mentioned in the paragraph? Of course, it's a sneak peek as to what's to come without coming out and saying it. As an illustrator, it's fun to add these personal touches and vision to the flow of the story. Also, with no direct specifications to how many pirates, gender, and clothing designs it provides more room for the illustrators imagination to take shape with the story.