When the World Wide Web began there were not very many pages that one could obtain information from. As the web increased in size many website URLs started to become rather unwieldy since you could have nearly infinite number of subfolders on hosts.
With this you could have a URL similar to
Who is truly going to remember a URL like that?
Or something similar to
If you wanted to create a URL that would be easily remembered, or to be used on a service like Twitter, you can use a URL shortening service like bit.ly or j.mp.
One of the issues that can potentially arise from a URL shortening service is that you cannot always verify where the short URL will ultimately lead. In order to combat this Twitter monitors what URLs have been reported as spam and protect users who use their t.co shortening service. Twitter is no longer the only company using a short url like t.co. Google has now acquired g.co.
Google is going to use g.co as their official URL Shortener. However, instead of using g.co to go to any website on the Internet, Google will be using their g.co domain to only go to their own Google services. The use of g.co to officially go to Google services will allow Internet users to verify that any g.co URL is a valid and malware free link to a Google service. Imaging being able to go to Google+ by typing in g.co/plus. It would be much easier than typing in plus.google.com or google.com/plus. It may not a big change, and it may be transparent to most users, but it is a step in the right direction to making the web a lot safer.
Source: Official Google Blog