If you have the Jetpack plugin installed on your WordPress blog and the “WP.me Shortlinks” module is enabled, WP.me shortlinks will be generated for each one of your posts, pages, and attachment pages by default.
Hence, whenever you edit an existing post or page and click on “Get Shortlink” button, you will get a shortlink that includes the wp.me domain, whose functionality is similar to other URL shortening services.
If you prefer a shortlink that contains your domain name and not the WP.me url, then you have to deactivate the “WP.me Shortlinks” module via JetPack settings.
Once deactivated, you will be reverted back to use the default WordPress URL shortening feature. What the default WordPress URL shortener does is simply replace your full permalink with the post or page ID.
Note that either way though, using the default WordPress URL shortener or the Jetpack powered WP.me option, you do not get the benefits of tracking or custom branding that some URL shortening services offer.
Kudos to +Desmond Nwosu for the tip.