[swilliamsio]

Twitter's link shortener gets tonnes of use. Seems like every external link in every tweet is converted to a t.co link instead to save characters.

[SalimoS]

I’m sure that the real reason for Twitter to use t.co is analytics and more control over the platform.

[playpause]

That’s just Twitter’s redirection proxy. It’s not people using it as a URL shortener. It is Twitter automatically linking all URLs in tweets to go via t.co for tracking.

[dewey]

No doubt that it's used for tracking but "clicks" on the URL could probably be measured in other on-page ways too. One additional reason is probably that if there's a spam URL detected they can just block the short URL and the problem goes away instantly.