It's a known fact, but nevertheless annoying that Twitter URL LENGTHENS, and annoying that Twitter thinks it's ok to rebrand publisher shorteners like nyti.ms or tcrn.ch which help users recognize where the redirect will take them.
Twitter even shortens things that you didn't intend users to be clicking through; it you want to tell people to connect to your IRC server or want to talk about a host name redirection issue, you're screwed.
But these publisher specific shorteners no longer serve any function surely. They were because you had to use a shortener, so they created their own. Now everything goes through t.co you effectively do not need a shortener yourself. For your own site you get no more analytic data from a shortener than a real url.
I don't generally use sharing services; I email links while reading the page. I like emailing a link that I know doesn't line break. That just needs to be less than 70 chars, but many news sites are longer. So as long as they're shortening, might as well shorten for all venues. Twitter's shortener is useless in this direct sharing case.
Another publisher specific function is, as I mentioned, letting a user know through your branded short URL what this shortened link is likely to take them to.
