You're given a short URL such as http://is.gd/w
How do you know exactly where this URL will take you? Is the URL likely to be from a legitimate site? Or it is a site known for phishing, malware, or viruses?
LongURL will expand the short URL into the full, original link, so you can see exactly where you would be directed to before clicking on the link.
Thanks to my colleague who shared this tip on the staff intranet where I work.