This declaration corresponds to the center environment.  This
  declaration can be used inside an environment such as quote or in a
  parbox.  The text of a figure or table can be centered on the page by
  putting a \centering command at the beginning of the figure or table
  environment.

  Unlike the center environment, the \centering command does not start
  a new paragraph; it simply changes how LaTeX formats paragraph units.
  To affect a paragraph unit's format, the scope of the declaration
  must contain the blank line or \end command (of an environment like
  quote) that ends the paragraph unit.