Hallway pages are used for submissions to Search Engines that use 'Spiders'. Spiders are robots sent out to visit your website by Search engines, their purpose is to gather information about your web pages.
Recently some major search engines are scoring pages higher that have been found by search engine spiders as opposed to submitted pages.
When the hallway page is submitted to a search engine, the search engines spider follows the links on that page and indexes the pages you really want indexed. The pages it inspects via the hallway page should rank higher than they would if they were submitted separately.
