Don't take my word for it, that's how Twitter described it when they launched it here: https://blog.x.com/en_us/a/2012/shutting-down-spammers
From a scale perspective it also seems a lot easier to remove one redirect from happening vs. finding every Tweet that contains a certain url you want to remove.
> Additionally, we now use our link shortener (t.co) to analyze whether a tweeted link leads to malware or malicious content. This helps us prevent users from visiting malicious links and helps us shut down hundreds of thousands of abusive accounts.
