People put effort into creating short URLs, but is that necessary anymore? They're only ever used to post to Twitter. Where else do we see them? (Sometimes linked to on websites. More on that in a bit). I'm going to list the purposes of short URLs:
save characters when microblogging. This is no longer necessary on Twitter, where URLs take up 22 characters no matter how long they are.
obscure where the resulting link is going to. Unless you look it up using their API or something like LongURL.org, you can't, just by looking at it, tell where a link is going to go to. Twitter expands links internally, so searching for a URL string (that isn't bit.ly) will reveal bit.ly links, for example.
track click-throughs. ow.ly (Hootsuite's URL shortener), bit.ly, and others, let you track how many people click through. Presumably with shorteners like ht.ly (also by Hootsuite, but it puts the link in an iFrame) can track information like browser type and other information. This must be the predominant reason why people use short URL links in websites even though there's no shortage of space to put them in the HTML.
tell you which client people are using to post to Twitter. ow.ly/ht.ly means you probably posted from Hootsuite. buff.ly means you probably buffered the tweet (using Buffer). Instapaper has its own short URLs, using the instapaper.com domain, so that means you probably shared it from within Instapaper.
vanity or branded shorteners look cool.