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.