Particularly when you are trying to share a page and do not have access to the analytics, creating a shortened URL allows you to gauge the success of your link sharing.
These services are free and some allow the user to generate a custom alias–which can be helpful if you prefer vanity URLs.
After all, what is more attractive to click on, http://www.example.com/this-is-an-example-link-00-23543-123543543534 that is several characters long and will take up a considerable amount of room on social networks, or this form http://bit.ly/1K7joDC?
Generating a shorter URL provides your viewers with a more manageable and shareable option.
Think about it, Overstock.com pushes O.co for a reason.