Let's say we have more than 80 pages and groups on Facebook. When you share the same post on all those pages and groups, Facebook might consider posts as duplicated posts, and you might get a warning by Facebook.
By enabling the "Unique post link" option, the ending of each link gets random symbols.
As a result, the post becomes unique, and you can share the same post as many pages or groups as you want.
The plugin has the option to shorten your Post URLs with TinyURL or Bitly services as well.
The "Additional URL parameters" option allows you to add ready keywords on your URL parameters.
The "Share custom URL instead of WP Post link" option allows you to define and type your custom post URL using specific keywords. You might need it if you want to share a different URL than your post URL.