My reading takes me through various links and sublinks and cups of coffee, and has led me to some information and a wee moment of a-ha which I think is important enough to share.
The information pertains to URL shorteners, the service offered by sites like TinyURL, MakeAShorterLink or budURL. These services are for those times you want to share a long, hairy link with someone, without risking it being ruined by a mandatory line break. However, this was a problem for older e-mail and news programs which would have a fixed line length. Now the problem seems to be the URL shortener itself. Let me quote Joshua Schachter, whose post on URL shorteners inspired me:
[T]he biggest burden falls on the clicker, the person who follows the links. The extra layer of indirection slows down browsing with additional DNS lookups and server hits. A new and potentially unreliable middleman now sits between the link and its destination. And the long-term archivability of the hyperlink now depends on the health of a third party. The shortener may decide a link is a Terms Of Service violation and delete it. If the shortener accidentally erases a database, forgets to renew its domain, or just disappears, the link will break. If a top-level domain changes its policy on commercial use, the link will break. If the shortener gets hacked, every link becomes a potential phishing attack.
The above paragraph has a number of links in it on the blogpost I took it from (so go there and get wise), which I followed, and that was what gave me my a-ha moment: The technology of the shortcut relies on a database owned by the site making the shortcut. If anything happens to that site or its database, for any reason (several are listed in the quote above), the URL is useless. Joshua points out that today's e-mail programs don't need to be concerned with line breaks in links. If the idea is to avoid a long, hairy URL in an e-mail (or on a webpage), don't. The link can too easily die.
There are other reasons for the advice not to use: You prevent the user from seeing where the link is going at a glance (when they hover their mouse over the link, say), and you also have no control over that third party, the middleman, the one making and converting the link for you. That third party may change its terms of service or could add ads. Or get banned. Because spammers make use of shortened URLs, one of the trailblazers in the game, TinyURL, has found itself banned a number of places.
What seems like a helpful idea (enjoying increased popularity recently due to Twitter's limitations), should probably be used as little as possible. Like maybe only on Twitter.