[TheSmiddy]

Once the link shortening service knows it's a scam they can redirect you to a "saved you from being scammed" page.

(although evidence of this happening in practice hasn't crossed my radar, but it's probably because I just don't click those links in the first place)

[eridius]

You don't need a link shortening service for that. The website and API can just start changing the URL it includes in the tweet if it determines the original URL is a scam.

[megous]

They can redirect you anywhere. They can also rewrite anything in the URL, like add affiliate IDs or whatever. I'm sure some of them do that, because why not.