Often each chapter in a book starts on a right page, as well as the title page, index etc.

• If the previous chapter ends on a left page, you can start a new chapter on next right page.
• If the previous chapter ends on a right page, then a blank (left)page is inserted,  so the next chapter can start on the right page.

It is unusual (but not prohibited) to insert two blank pages, in which the front and back are empty.