Many users on social network use the short link services which comes to reduce the URL of the shared link. this helps on certain website such as twitter where you are allowed to post only 140 characters per post. on the other hand and from the security prospective this may involve negative points such as hiding the true URL of the page and affect the integrity of the network, using personal data and impact on person privacy by selling information to advertisers.
Another point the service can be switched off at any time and your link will not work and also as a negative point there is a delay in opening the required web page and add additional time to website loading. this delay because users are redirected to several website till he reach the true URL.
Today there is a new service that is very interesting and will make more user avoid the shortened URL services. http://shrturl.co/ allows you to create a fake modified copy of any website. you can for example edit the page to add some titles, text and replace image to friends. the page will be hosted for 48 hours but it allows you to make it in your awareness program to demonstrate how it will be easy to fake users and make a modified webpage.
For your security never click on a shortened link that you are not sure where it is leading because this may infect your computer and redirect your browser to a malicious website. if you need to open a shortened link use long-URL (http://longurl.org/) service that will expand the shortened links.