The Views Litepager module solves a problem of scalability for sites with large amounts of content. Drupal's core pagination system creates a pager navigation that shows exactly how many pages of content exist for the content list. This requires that a COUNT query be executed based on the query used to generate the list.
While COUNT queries are blazingly fast on tables with MySQL's MyISAM engine, they are painfully slow when using InnoDB tables which is the recommended engine type for high traffic Drupal sites. The COUNT queries quickly degrade the more rows a table has.
The Views Litepager module solves this problem for Views pagination by providing a pager option that does not require a COUNT query to be executed. This "Lite" pager is only slightly less useful than Drupal's core pager in that it does not allow you to navigate to the "last" page and does not show how many total pages of content there are. But for large sites, this small cost in features is worth the boost in performance by ridding your pages of the painfully slow (and sometimes crippling) COUNT queries.
UPDATE: This module can now be found on Drupal.org.