I read the description of Global Redirect and Path redirect, but I still don't understand what the difference between the modules is, and why Path redirect recommends Global Redirect.
What is the difference between the modules?
Global Redirect searches for an alias of the current URL and does a 301 redirects to it if found. This prevents content from being displayed on multiple urls when the path module is enabled. Displaying duplicate content at multiple url's can cause a loss of search engine site ranking.
Path Redirect allows you to specify a redirect from one path to another path or an external URL, using any HTTP redirect status. This is important if you want to change your url scheme for some reason and you don't want to break all exisiting links (search engines, user's bookmarks etc.)