With the spread of micro-blogging services, there is a change in the way URLs are conveyed. Long URLs tend to get unwieldy for use on micro-blogging services and hence the URL shortening services that make URLs succinct but in themselves meaningless.

There is an article up at SEJ that summarizes the benefits and disadvantages of the same.

To quote from the article:

* use the services when you can't do without them (e.g. with Twitter and Twitter applications that automatically shrink a long URL using TinyURL);
* use the services when you don't care if the link will be clicked or who it will be clicked by;
* don't use them at your own site.

The use of URL shorteners does not have any advantages as such.

A list of URL shortening services can be obtained from here.

Its a great feature to use when one wants to convey a specific site within the constraints of the character limit.