When you have a large body of text you want to make it as appealing as possible. This makes it easier for your reader to absorb the messages that it is sending. This concept is especially important in journalism as the most relevant news is pushed to the top. It's about maneuvering layout with typography to make it appealing and easy for your viewer.
But it can be about more than that as well. The written word can often convey a feeling or an emotion that you want your reader to be able to experience by simply looking at the page. It depends on what is in front of you.