URLs are getting longer. Sometimes, the address of a web page can run to hundreds of characters, large chunks of which are meaningless strings of random numbers and letters.
Such URLs are impossible to type, when you're following a link in a printed document. And even if you're including them on a web page for someone to click on, their sheer length makes the page look messy. Which is why many web sites, including this one, have started using the services of URL-shortening sites such as Bitly.
But here's the problem. How do you know where the shortened link is going to take you, if you can only see the shortened version in your browser and not the full unexpurgated version?
In the case of Bitly, specifically, the answer is simple. Copy the shortened URL into your browser's address bar, add a plus sign (+) to the end, and then surf to that address. You'll find yourself at a page which tells you the full address, gives you a summary of the page you're heading to, and even gives you some stats about the shortened link such as how many people have clicked on it in the past.
Neat, eh? Try it with one of the Bitly links that you probably have in your browser history. Just press Ctrl-H to see the history (from within your browser) and search for bit.ly.