This is what I do on my website. External links change or break all the time. It's a lot easier to change where a URL points to than to update it on some 300 pages.
Since these are 302 redirects, Google somehow started listing some of them. Many of those are affiliate links, so I'm wondering if this could lead to additional revenue.
Short link services will also let you redirect to different destinations based on rules. So you could split traffic 50/50, you could send European users to a different URL, etc.
Another valuable service is that they you let track clicks without having to add tracking code to the destination page, which means you don't have to modify the destination or even own it.
It's not really about link shortening, it's about dynamic redirects and tracking.
You could imagine a site having a URL for a game sale like "shortlink.com/gamesale" and right now a user in London would get sent to "gamestore.com/european-version-of-sale-page?tracking_param=may-2022"