Do not use this module; it is no longer supported. Consider using Path Redirect instead.
Legacy Path is intended to support websites that are moving to Drupal but have content that either won't be managed by Drupal immediately or at all, but must remain reachable through it's original URL. The assumption is made that the legacy system remains operational, but at a different (sub)domain or directory.
Note per #236414: Module does not work with 'Normal' caching enabled. that this module does not work with Normal caching enabled.
For example, an online newspaper might have an existing archive system that provides permalinks such as:
http://paper.example.com/content.php?section=12&article=22
After a Drupal installation, the online newspaper has moved the old system to the URL:
http://archive.example.com/content.php?section=12&article=22
This module accomodates redirecting (using HTTP redirects) the old URL to the new URL.