The chapter structuring commands divide a document into a hierarchy of chapters, sections, subsections, and subsubsections. These commands generate large headings; they also provide information for the table of contents of a printed manual (see section Generating a Table of Contents).
The chapter structuring commands do not create an Info node structure,
so normally you should put an @node command immediately before
each chapter structuring command (see section Nodes). The only time you
are likely to use the chapter structuring commands without using the
node structuring commands is if you are writing a document that
contains no cross references and will never be transformed into Info
format.
It is unlikely that you will ever write a Texinfo file that is intended only as an Info file and not as a printable document. If you do, you might still use chapter structuring commands to create a heading at the top of each node--but you don't need to.