In a longer or more complex document, you often want to vary the style or content of your headers and footers. Each section maintains its own headers and footers, so by breaking your document into sections, you can vary the headers and footers in each. In fact, you can manage the first, odd, and even page header and footer in each section.
Header and footer content
If you want header and footer content to vary in a document, break the document into sections. For example, if you want Chapter Five's header to read "Chapter 5" while the Chapter Four header reads "Chapter 4," you would need to be sure you inserted a section break between the two chapters.
Page number style (i, ii, iii, iv or 1, 2, 3)
If you wanted the introduction of your document to number its pages with Roman numerals (i, ii, iii, iv, etc.) you would insert a section break at the end of the introduction so you could set the page number style for the remainder of the book as Arabic numbers (1, 2, 3, ...).