It allows twitter to easily track which links you're clicking on, which some might consider to be a violation of privacy.
On mobile, t.co makes it so that you end up always launching a browser before launching the appropriate application (i.e. YouTube)
When you copy and paste and send a link to someone, they have no (easy) way of knowing what you're sending them without description or visiting, and it gives Twitter a mechanism for tracking who you send the link to. (One could posit a "malicious" tracking twitter where they serve up t.co links to people which are dependent on the logged in user to track that user's social network... fortunately I don't think this has happened yet.)
And as someone not in the U.S. with an unreliable ISP, t.co just flat-out times out half the time unless you modify your DNS settings to point to OpenDNS or Google or something.
I understand the value of being able to track click-throughs and quantify virality or whatever, but there really needs to be a better way to do this.
I've seen a similar thing with related services (mainly Google - although they appear to have removed it for a 'ping' now). I'm not exactly sure what causes it, but my browser gets stuck on "Waiting for t.co...". Refreshing the page just takes me back to the page I clicked the link on.
The fact that t.co don't have global servers probably doesn't help, in Asia and Australia ping times to t.co are 250ms+. Even in Europe it's over 100ms.
I can confirm this - I've stopped clicking links in the official Twitter client on Android when I'm outside in Australia, Australian mobile Internet is already slow, combined with t.co's huge latency all links just time out.
Even without those conditions, it's a problem. If I have too many tabs open in mobile Chrome, t.co will flat out not work. As soon as I "close all tabs", it starts working again. I have no explanation for this.
Why would your ability to resolve t.co be any different than your ability to resolve the actual host? If anything, it should be much easier to get a reliable DNS response for t.co.
It allows twitter to easily track which links you're clicking on, which some might consider to be a violation of privacy.
On mobile, t.co makes it so that you end up always launching a browser before launching the appropriate application (i.e. YouTube)
When you copy and paste and send a link to someone, they have no (easy) way of knowing what you're sending them without description or visiting, and it gives Twitter a mechanism for tracking who you send the link to. (One could posit a "malicious" tracking twitter where they serve up t.co links to people which are dependent on the logged in user to track that user's social network... fortunately I don't think this has happened yet.)