Structure and hierarchy reduce complexity and improve readability. The more organized your articles or web-sites are, the easier it is for users to follow your arguments and get the message you are trying to deliver. On the Web this can be done in a variety of ways.
In body copy headlines and enumerations are usually used to present the information as logically separated data chunks. An alternative solution is pagination, a mechanism which provides users with additional navigation options for browsing through single parts of the given article.