It is essential for providing spatial relationships between visual items, and actually guides your reader's eye from one point to another.
White space is an important layout technique often overlooked by the inexperienced designer.
While some artists concentrate heavily on what to put in, they can overlook what to leave out. A design that is to be visually appealing must also be easy on the eyes. Without an adequate amount of white space, text would be unreadable, graphics would lose their emphasis, and there would be no balance between the elements on a page. White space takes on an added importance on the web because more of a strain is placed on the eyes than with print material. You'll find that going through the same amount of web pages as print pages can be more visually demanding, one of the reasons being that you usually find yourself staring up at monitor flickering pixels coarser than printed ink.