Twitter writes that link length shouldn’t matter, but the zillions of URL shortening services out there show that, for now, it does.

But why?

There are two main reasons to shorten* a link:

• There’s a technical limit, such as SMS message length or email line width.
• You expect people to manually enter the URL.

Right now, with Twitter messages limited to 140 characters and links forced to share that space with the rest of the post, URL shorteners are critical. But they’re working on a plan to accept longer URLs, and specifically shorten them for SMS messages. The full link will be available on the Twitter website, desktop clients, and other platforms that don’t have that hard and fast limit.

That will cut down on the demand for shorteners, but they’ll still be useful.

For one thing, there are other microblogging platforms out there like StatusNet.

For another, there’s email.

IIRC, the first URL shorteners launched because email programs often break up really long lines, including really long URLs. In plain-text messages, that leaves links not just unclickable, but inconvenient even to copy and paste, because you have to copy each line separately and paste them together. This will continue to be an issue as long as people continue to put visible URLs in email.

And then there’s the human factor. It might not be easy to remember http://is.gd/cGE8V, but it certainly takes a lot less time to write it on a scrap of paper than http://blogs.discovermagazine.com/badastronomy/2010/06/07/hard-to-port-eject-goose-eject/.

Which of those URLs would you rather type on your keyboard? Or worse, on your mobile phone?

*In this case, I mean making it really short and cryptic. There are plenty of reasons to keep links readable and sort of short.