If you need to get out a message and find the URL link is too long to accommodate everything you have to say, the use of a URL shortening service allows you the wiggle room.
It's not uncommon to see the same URL root spread out among dozens of the Twitter accounts you follow - in this respect the shorteners are convenient and quick and, depending on the type of micro blogging service you use, automatic.
Users of Twitterfox, a handy Firefox extension that lets you track folks from a pop-up screen on your browser, will note that URLs too long to appear in posts are cut using one of the best known shortening services.
Some services have recently allowed users to customize the URLs, so the first string above could be also marketed with a name you choose.
The downside to this, for one, is that more popular names may be taken.
Good to use on the go if you Twitter constantly, but are shortened URLs good for your site's SEO? In observing recent trends in Twitter, it isn't difficult to see spam accounts are on the rise, and the inclusion of such a URL, however innocuous the preceding text may appear, could lead to a phishing link.
It stands to reason one should look on shortened links carefully, clicking through only if you are certain the source can be trusted.
The use of another company's URL root in your posts, aside from your own domain, might also set back marketing efforts.
The more people see your name, the more apt they are to remember your URL.
Long strings cut short risk the dilution of your brand as you micro-blog.
This is not to say you should never use a shortening service.
One suggestion, if you must promote long URLs for specific pages on your site, would be to use a service that lets you customize their link name.
Make a spreadsheet and record all the customizations - using your brand in every way possible - and drawing from that list as you Twitter.
With many services the shortened URL is permanent, so you can reuse them as needed.
Another suggestion for marketing via Twitter is to create alternative pages on your site with short file names that best describe the content.
This way, you can provide good text before your link and get everything in under the character limit.
URL shortening services are handy in a pinch, but ultimately it is important to promote your own domain in Twitter, Facebook, or other social networks.